Press: [F8]
Then carefully read the options you have during the update process.
Also:
If you’re woried about the results of any action in KiCad, then just make a backup before you do that operation.
Almost any operation can be undone with [Ctrl + Z]
Save your stuff before a “dangerous” operation. If it turns out badly and [Ctrl + Z] does not work, you can always still just exit KiCad without saving (But making a backup beforehand is a better option).
If you make a backup every now and then, it gives you ease of mind, and you have more incentive to do a “dangerous” operation. The worst that can happen is that you lost your time between the last backup and when *&^%$#@! happens.
Here are some more thoughts about intermediate backups:
In short:
Git is powerful, but takes effort to learn.
Zipping up the whole KiCad directory is simple and still effective.
KiCad has a built in “Archive” option in it’s Project manager.
It’s the same as Eeschema / Tools / Update PCB from Schematic [F8] and it basically does the same as creating a netlist and then switching to Pcbnew and loading that netlist (and new footprints) but then without bothering with intermediate files. Working with netlist files has been deprecated for several years, but It’s stubborn, and I see lot’s of beginners still using it. I even see it on beginner tutorials for KiCad on youtube.
This update process does not change parts that are already on the PCB (unless you tell it to do so). The dialog that controls the settings looks like;
And…
If you make a backup beforehand, there is no risk in just trying it.
I am wondering about your workflow though.
It is very common to have a lot of update cycles for the PCB from the schematic, but your first post suggests that you first drew a schematic, and then only once put the parts in Pcbnew. KiCad maintains the association with the schematic and the PCB, and this update process is (or at least should be) only an update of changes made. If your workflow in KiCad is not right, and this normal process does not work, there is indeed a risk that you loose some of the work you did in Pcbnew. But “not updating regularly” is then not the right solution. The solution is to “fix your workflow”. If you run into trouble here, then we are here to help.