Can I change from FC5 to UC5

It depends

FC = 64-bit
UC = 32-bit


You can run 32-bit IDS on a 64-bit OS, but you can't 64-bit IDS on 32-bit OS

Actually, I dont know about other OS's, but you can run 64 bit IDS on AIX with AIX in 32 bit mode. Defeats the purpose I know, but you can definitly do it because I inherited a shop where the ding-bats before me had deployed just that configuration. AIX will thunk up to 64 or down to 32 in many cases, including IDS. I have since set my OS kernal to 64 bit mode ni order to let the IDS engine run full steam.

Also while I am running the FC version of the engine, I am using a UC version of the tools for 4gl developement. This also was left over and I need to migrate to the FC version in order to build 64 bit 4GEs but I have not got around to it.