Trying to replace clutch or throwout bearing

I recently messed up my friends car and i am trying to find out what is wrong first and then how to fix it. I burned his clutch really bad and his car has a hard time in reverse more than any thing. he says it is leaking some sort of fluid he thinks clutc fluid and it drive like **** compared to what it did. It is a 2002 VW GTI 1.8t and stage 2 clutch. When i was driving it i smelt the clutch burning after i shifted from first to second gear and then soon after it stopped grabbbing gears so i coasted. After 20 minutes of cooling it was getting into gear again but never the same. Any ideas on what it could be and how hard to replace? any answers would help alott .

thanks, Brent