You do not have to disassemble any of our shifters to replace the cable. Instructions can be found here. To summarize, using the upper shift lever, shift all the way into the highest gear (smallest cog). Remove the cable cap* (marked in red). Undo the cable fixing bolt on the derailleur. Remove old cable by pushing the cable head through the cable port. Route the new cable, narrow side first, into the cable port and out through the barrel adjuster. Make sure the cable head is fully seated.

*Some shifters may not have a cable cap; in that case the cable port sits next to the upper shift lever.

Verify that your b-tension screw is adjusted properly. The adjustment should allow for an 11-13mm gap for Acolyte/Advent and a 15-17mm gap for Advent X between the guide pulley and largest cog of the cassette. If that adjustment cannot be made, there is a good chance that your chain is too long.  Most derailleur cages are eccentric.  As the cage is pulled towards the chainring, the guide pulley is then moved out of the way of the larger cogs of the cassette.  Too much slack in the chain will allow the guide pulley to rest on the largest cog.

Remove the clutch cover with a Phillips head screwdriver. Tighten the clutch bolt with a T15 torx at quarter turn increments. This will add pressure to the friction washers and strengthen the clutch. Clutch strength can be tested by hand throughout the process.