I was monkeying around, trying to change my grub screen graphic. After playing around a bit, it became apparent that I could not find a simple tool to do so. So after a bit of reading and trial and error, I found a pretty easy way to do it for the KDE version. I hope this helps someone.
I'm writing this for newbs like myself, so please don't think I'm trying to insult your intelligence.
1) Find the pic you want to use and open it in gwenview, or gimp. Using the Image>scale command, scale the pic to 800x600 and save it as a .jpg to your desktop (or wherever you like).
2) While still on your desktop, right click and select create new > folder and name it gfxtest
3) Open your file manager...dolphin, konqueror, or whatever you use (I'm keeping the command line out as much as I can...) and navigate to root/boot. You'll see a file named gfxmenu. Copy it to your clipboard and paste it into the folder you made on your desktop (gfxtest). Close file manager, simply to keep things neat.
4) Open a terminal window (this part isn't hard, just copy the commands I write and paste them in your terminal...don't copy the press enter part...you don't even have to type anything....) and beside the prompt paste:
cd Desktop/gfxtest then press enter
cpio -i < gfxmenu press enter
Close the terminal
5) Open the gfxtest folder on your desktop and you'll see lots of little files appear. Find the gfxmenu
file and delete it. Next find the back.jpg file and delete it. Minimize the window.
6) Remember the pic you saved way back at the beginning? (the one that you want to be the pic for the GRUB background) Find it and copy it to the clipboard.
7) Maximize the gfxtest window again and paste the pic from your clipboard in the gfxtest folder.
8 Rename the pic to back.jpg , and close the window WE'RE ALMOST THERE!!!!
9) Open up a terminal window again (last time) and paste this command
ls . | cpio -o > gfxmenu
press enter and close the command line (phew, that's done!!)
10) go back into the gfxtest folder on your desktop and find the file named gfxmenu, copy that file to your clipboard
11) Open your file manager as root (if you're unsure how to do this, open the file manager, right click on it, click on root options and click open as root)
12) Navigate to the root/boot folder, find the file named gfxmenu and change it's name to gfxmenu.old (right click > rename), then paste the gfxmenu file from your clipboard to the folder.
13) Lastly, close any open windows that may be left, delete the gfxtest folder from your desktop, reboot and enjoy your new GRUB pic.
These steps worked for me, I hope they help you, too.