You should always make a backup of your Nand/Nor Flash.
If you're already on CFW, you can always start with the 2 (optional) steps below before installing the CFW of your choice:
Dump your NOR/NAND Flash:
Install latest version of multiMAN CEX, plug in a FAT32 formatted USB flash drive into the right USB port, launch multiMAN under the Game column and go to mmOS > Press on any file > Open in HEX viewer > Press SELECT > Press START > Export GameOS LV2: Select No > Export HV LV1: Select No > Export FLASH: Select Yes
This creates a backup of your NOR/NAND flash so that you can recover using a hardware flasher in case of a (highly unlikely) brick. It is recommended to do it every time you upgrade/downgrade your CFW just in case something goes wrong.
Dump your eEID Root Key:
This has to be done only once, while (and if) still on 3.55/4.50 CFW, just in case you want to ever switch to DEX in the future without having to downgrade back to 3.55/4.50 CFW to dump it.
Install eEID_RKDumper.pkg > Unplug all USB devices > Launch eEID RKDumper under the Game column. It will black screen for 10-15 seconds, beep 3 times and reboot automatically. Now FTP to your console and retrieve your Root Key/PCK1 (48 bytes) from /dev_hdd0/tmp/eid_root_key if on 3.55 or /dev_hdd0/game/FLTZ00010/USRDIR/eid_root_key if on 4.50. Once you retrieve your Root Key, you can delete eEID RKDumper from your XMB as it is not needed anymore.
You should also run QA Flag as well [Register or Login to view links]
Once that is done, you can update to any CFW of your choice.