Ronnie is correct, almost, As you have an HMI on the system then uploading the data memory (usually called Main) is almost certainty, the reason for this is that there is probably some variables (set points) that can be set via the HMI for example speeds, recipe variables etc. If you do not update these on your PC then should you loose the PLC program you will have to re-enter any variables as above. I also suggest you do not just upload to a blank file, I believe you have a copy of the original anyway on your PC, I suggest you save this as an original backup. Then take a copy open it up then upload the PLC to that file and save it as a different filename (conventions are often original file name plus a current date & version number). This way you keep your original (just in case), your re-named file that is updated with any possible changes & data becomes your new working file, this is important because uploading to an empty project you will have no symbols or rung comments.
So as per these steps:
1. Save a copy of original (if you have one).
2. re-load it and update it so you have incorporated any possible changes or modified data then save it as the latest version by an upload of everything.
3. Do this again and save it with the latest version number.
If you intend to make changes use this file but again save it as a working file with another version number in the filename.
4. use this latest one to do your changes.
5. Some time after a well tested system you could delete some of the previous files.
Every one has different ways of version control and I'm sure this will attract loads of comments etc. but a simple way is to incorporate version control is in the file name.
for example:
Original file, "Production line 1 20_01_20 V1.0"
Original plus upload "Production line 1 24_01_20 V1.1"
New modified one ""Production line 1 28_01_20 V1.2"
I also suggest you add comments at the first line of the program stating what the reason is for i.e. "Updated original with data upload V1.0"
"Changes to code for xxxxxx 28/02/20 V1.x"
Make sure you always have a way back should things go pear shaped.
Keep backups on a separate media i.e. a server or some form of removable media.
