Editing PDF encounter maps using GIMP(not sure if right forum)

Hey guys, I'm kinda new to DMing(been playing though) and I've got a quick question regarding encounter maps. I'm trying to use the maps that come with the campaign module PDFs that I got from Wizard, and I can't seem to figure out how to use GIMP to get rid of the enemy markers on the maps. They're letters H, K, etc. I'm sure somebody here has used those maps and uploaded them to roll20, which is what I'm trying to do.
If anybody out there can help, I'd greatly appreciate it. Thanks ahead of time.

I remember using PDF maps with the markers to. If nobody offers anything else...
What I did was take the blank tiles of the map that looked like they matched the pattern and made those into an image to paste over the enemy markers. So something like the squares next to it so it would be exactly the same square. Kind of a jury rig. It leaves something to be wanted but most of the times it looked good enough.
With gimp you can also take one of the blank tiles of the map and make that an image in the pattern fill, and with the pattern fill of the "dungeon tile" make things with dungeon tiles as the basic floor...although I'm not sure if the pattern would fit the gimp grid.
I suppose you could also get everything except the floor off the maps and just change the floor entirely to what's in gimp pattern fill, if you want it to be more complete but that is more work.

Try to patch the markers over with adjacent squares or whatnot. Usually worked for me. Along the same vein if it looks strange doing only one you can copy 4 or 9 squares or any rectangle and use that to paste over it.

Thanks for replying.
That's what I was doing, but then I was reading all of the other campaigns, and holy hell, do some of those look hard to edit. Haha.
I guess I'll have to be creative. I was hoping there was some super special expert technique I couldn't figure out.