EDIT: For those of you who want to make legit, super powerful mega charged pokemon, go here. It's a pokedex with all the pokemon and stats and everything you need to know. In other words, check out the pokemon you want to create, make only a couple of the stats maxed out for that pokemon. For example:
Raichu = make Special Attack and Special Defence stats really good because that's closer to normality
Garchomp = make Attack stat really supercharged because it can.
DO NOT SUPERCHARGE LEGENDARIES because now, that's just cheap, rigged,and downright virtually imposible.
Oh, and for that link, there's also a whole bunch of goodies that will help you on your pokemon journey and hacking :). Okay, maybe just journey, but things like damage calculator, balanced team tester, etc will help you lots.
Step 1: Opening a File
plug in your R4 and open the file from the pokesav by clicking OPEN and going to your R4 memory chip.
Step 2: Fiddling Around With Poksav and Your Sav File
you can do LOTS of stuff with pokesav, like change:
amount of money you have
your rival's name
and many, many more...
Step 3: Changing Your Pokemon
if you have an empty slot in your party, you can make a new pokemon from scratch, but you cant change the sprite. i'll show you how to CHANGE a pokemon's stuff.