Just follow the written upgrade instructions from any v6 forum. The only change might be if you have added other modifications that add extra profile fields: ie: the calendar added profile field #55.
If you did, you'll need to search in ubb_lib_files.cgi for maxmemfield and increase that number (31) to whatever number profile fields you have.
Other than that, just overwrite all files with the upgrade set of files, and follow the rest of the upgrade instructions.
