Using xDelta to Patch ROMs
xDelta is a program which takes 2 files. Your original unpatched NDS file and a patch file usually called .xdelta. The interface looks like the following.
In the first box titled Patch you select the patch file you downloaded from RomUlation or elsewhere.
In the second box titled Source File you select the unpatched ROM that you want to patch.
Finally, in the last box titled Output File you browse to where you want to save the patched file and then you type in a file name like in the following screenshot.
Once done just hit the Patch button and xDelta will create your newly patched game which you can then transfer to your flash cart or play in your favourite emulator.