well there are different types of patchers out there some cut out things that are need sme only work on roms of a certain size so first thing to do is research the patchers out there
PatcheRL available from romhacking.net by Sephiroth87 I've only tried to use this once after a file compare not what I wanted, you might have a different experience
IPS not recomended for use on ds roms have tried always comes up with an error
Lunar IPS not recomended for use on ds roms have tried always comes up with an error not designed for the ds
PatcheRL by Sephiroth87 have tried not my thing you might have a different experience (is designed for the ds)
xdelta UI by KaioShin - have used is my preferred patcher

PatchROM have used not designed for use on nds roms
NINJA 2.0 by D Haven't used it cannot review it
FEP "Tool for applying FireFlower format patches. FireFlower is a textual patch format often used for graphic or color hacks." Haven't used it cannot review it
FPM "Tool for creating FireFlower format patches. FireFlower is a textual patch format often used for graphic or color hacks."Haven't used it cannot review it

there may be others so do a search

as to how to image hack well...
there is a topic on this already ds specific please use the search button
but try aalso the wiki http://gbatemp.net/index.php?showtopic=73394&hl=
topic on 2d grapchic hacking not much help http://gbatemp.net/index.php?showtopic=73394&hl=
for quick question on how to http://gbatemp.net/index.php?showtopic=102426&hl=
for extraction http://gbatemp.net/index.php?showtopic=110950&hl=
how to translate http://gbatemp.net/index.php?showtopic=70348&hl=
crystaltile2 specific image insertion http://gbatemp.net/index.php?showtopic=193033&hl=
to post for help http://gbatemp.net/index.php?showtopic=79250&hl=