I just updated firmware in a 1756-L75 from 20.x to 32.x. I don’t guarantee any of this, your mileage may vary. Check things yourself, take your time, don’t screw this up as it will be very expensive to fix. A few tips to make life just a little bit easier:

• Make sure both RSLogix 5000 and Studio 5000 are installed on the PC you’re going to use (RSLogix 5000 v 20.x and Studio 5000 v 32.x) or whatever
• Download ControlFlash Plus 5+. ControlFlash 15 or higher is required but they’re both kind of a pain. I think you get a little bit better feedback on ControlFlash Plus.
• Put your downloaded firmware files (.zip) into the C:\Username\Downloads\RA folder, this should be one that is setup for scanning if you look in CF+ settings. Refresh firmware when you first start CF+ if you haven’t already used that particular firmware. If you get errors about the DMK, ZIP or file signatures or whatever, just download the absolute newest version of CompactFlash Plus. Rockwell is not user friendly.
• You’ll need to connect to the PLC with the old v20.x software and place it in remote program mode.
• Our network configuration is really jacked up so you might have to look for other paths in FactoryTalk Linx or RSLinx for CF+ to update the firmware versus how you normally connect for monitoring or troubleshooting. From what I can tell as long as the path can connect to the PLC in question, it can update it
• Before you do anything else, though, load the current ACD file into RSLogix 5000 and then change the controller version from 20.x to 32.x. This will prompt the system to load Studio 5000 with the new firmware level. Save this file with V32 in the filename just to make life that much easier (it will also be automagically updated but a file with an extension of acd_v20 will be saved too). As it does the conversion watch for any errors; messages and such might be trivial but actual errors need to be understood prior to upgrading.
• Note that your program will be deleted after CF+ is done. You’ll need the version you saved from Studio 5000 to download to the CPU, otherwise there will be no program.
• AOPs/AOIs seem to carryover between versions. I didn’t have to reload or download these, but there’s really no telling what’s going on in the background.
• Before the conversion, I downloaded every conceivable option from Rockwell. Their engineering groups don’t appear to talk to each other at all so I highly recommend you assume that you need every single app, firmware, file, AOI, AOP, etc., that you can possibly find. You might get lucky but I’d lean towards being screwed.

If the firmware update that it’s successful, download the Studio 5000 v32 saved earlier and then place the PLC back in remote run. The easiest thing is to see if any I/O not responding or other flags for issues. If the processor returned to remote run mode you’re probably ahead of the curve. Start testing…