are you using IVR non-NAT, if you are you need to convert to IVR-NAT before you go to 5.2. Other than that you just follow the normal procedure, look at the release notes for each firmware to make sure your hardware is supported and then do the usual
install all system bootflash:m9x00-xxx.bin kickstart bootflash:m9x00-xxx-kickstart-xx.bin
as a side note, i know you don't mark people replies to your questions as helpful/correct on EMC ECN ..at least do it here to show your appreciation.
@dynamoxxx
@dynamoxxx