Here is how I took my X-treme xb 600 from 48v and 21 mph to 60v and 30 mph. First, you will need to remove the battery pack and seat. Also, take the lid off of the battery pack and make sure all the connection screws are tight(some of mine were loose). Next, drill (2) 1/4" holes in the corner of the seat pan in the left front corner. See Below...
I finally got around to documenting the process for those still unsure of the process. Hopefully this will help a few people out who still aren't sure of the procedure.