Hi
I replaced mine last year. Mines an 1980 LHD version and it was relatively easy. Make sure you get the right cable as they are different lengths! I also replaced the pipe the cable runs inside, just because mine was original and they're peanuts to buy compared to the ease it makes threading the new one through, plus you know you won't get a sticking cable due to build up of cr@p.
Basically, drop the spare wheel and get under neath to find the connection to the pedal. You need to remove the "box" that protects everything. You'll see the connection attaching the cable, and make sure you take note of how it's put together! Pictures on your phone will help a lot. All you need to do is find a path from here to the rear and thread the tube through (or use the old one and tape to it and pull through, but you'll need to ensure you unclip all the clips first!
Rear connection is also simple but again take pics etc so you know how it goes together. Setting up can be a little tricky as you nned to make sure you leave a little slack in the cable so as not to be opening the carbs up slightly with no foot on the pedal.
Have fun

T25 Westfalia 2.0l Aircooled 1980 in a nice beige colour with a bit of antique steel thrown in