The easiest DIY suspension modification on a 993 would be shocks,spring and sway bar upgrades.  If you are just replacing the shocks or springs the only special tool you will need is a spring compressor.  If you are replacing the complete coil over unit and the new unit come already assembled you will not need to use a spring compressor.  A 4 wheel alignment would be necessary once everything is put back together. 

I used the impact gun in my DIY because (1). I do not have this special open socket wrench, (2). I have been using this impact gun method for years without any problem. (3). Through hands on experiences I have had I can pretty much apply the correct torque setting free handed. .......Although I own three different torque wrenches... 

For first time DIY people I do recommend that you purchase the right tool prior to this DIY, the danger of using an impact gun to tighten the top shock nut is that you might apply too much torque and strip the thread the also break the shock shaft. 

(2). Remove the brake line clip that is on the shock.  At this time you will want to modify the brake line holder with a Dremel tool so that there is an opening for the brake line to slide out from.  I found by doing this to be much less time consuming since you don't need to bleed the brakes afterwards.

(3). unclip all the wiring from the brakes sensor, ABS sensor to the round harness, and move the round harness away from the shock at the right side and the back of the shock. 

(4).  (You will only need to do this part of the procedureif you are installing new springs or shocks only.)  Loosen the large 21 mm bolt on the center of the shock near the shock tower.  But do not take the bolt out completely. ONLY LOOSEN IT. I used a impact gun to do this, if you don't have a impact gun you will need to get a special Hazet half open socket tool that will allow you to stick a hex key down to the center of socket to hold the shock shaft while you loosen that nut.  Or you can ask someone with a strong grip to hold the shock shaft in place to prevent it from spinning while you loosen the bolt. 

(5). Loosen and remove the two bolts that secure the shock to the hub assembly.  These are two completely different size bolts, one is a 10 mm allen bolt the other is a 17 mm bolt, so there is no way to put them back in incorrectly.  The 10 mm allen bolt is used for camber adjustment, while the 17 mm bolt is to secure the shock from moving after the camber adjustments are made.  After you have installed the replacement shock and before you tighten the these two bolts you will need to push the top part of the hub assembly including the rotor all the way inward toward the car to give yourself the maximum negative camber, since there is no way for most people to set the correct camber without the right tools.  This is the only way to ensure that the camber is matched on both side of the car before you drop it off at an alignment shop.  Of course you could go the other way of maxium positive camber instead. 

(5).  Loosen the four 13 mm bolts at the shock tower that holds the shock assembly to the shock tower.  At the time the shocks will come off the tower and the hub by pushing down on the hub assembly.  Make sure you remember the direction of the red marking on the rubber shock perch.  When reinstalling the shock it needs to point back at the same direction.  And you should ask someone to hold on to the shock assembly from below before you loosen all the nuts.  In most cases the shock assembly will just drop. 

(6). Since in this project the shocks will be replace with a Koni adjustable shock so the plastic wire clips and wire harness mounts must be transferred over to the koni shocks.  You will also want to modify the brake line holder on the Koni shocks so the brake line can be installed back.

(7).  Now is also a good time to put the two shocks next to each other and make a comparison and make sure the replacement shocks looks exact the same as the factory shocks.

(8).  Install the spring compressor on the factory spring to hold the spring in place while you remove the large bolt on the top center of the spring perch. (Where I used a impact gun to remove the nut)  Once the large but is removed you can remove the shock perch from the factory unit and install it on the new unit with the new spring.  Again here is where the special Hazet half open socket will come in handy.

(9).  Install the new shock+springs back in the shock tower, and hand tighten the four 13 mm bolt on the shock tower.  At this time you will need to modified the original factory shock bolt (that bolts the shock to the hub assembly) holder if you are replacing the factory shocks with a Koni adjustable shock. Click here for detail.

(10). Reinstall the 2 shock mounting bolts, you will need to get a floor jack underneath the hub assembly to jack up the assemble a little at a time to get the shock to line back up with the hub assembly.  It takes some time to line them up, but once they are lined up you can get the bolts to go through with ease.  Tighten the shock mounting bolts and tighten the four 13 mm shock bolts on the shock tower.

(11). Reinstall all the wiring harness and clips.  Slide the brake line back to the brake line holder on the shock.  You are done! Completed installation picture!