There's plenty of tutorials, instead i will make a whole reply just for you...
First, the basic kit for what you need is;
**The frozen throne ( i hope you have it biatch )
**image extractor ii
**any image-editing software, im sure you have one, obviously...
Let's say you want to replace the attack icon,
* Open up Image Extractor II
* Goto View-->Search, and type attack... and search for the obvious name, it's "........BTNAttack"
Double click on it, you should see a preview to your right, if you don't, it doesn't matters, to the bottom of it you can see X and YResolution, both are supposed to be 64, it's the size of a normal icon.
*Save it to a .tga , at the saving screen you should see "BTNAttack", be sure to save it as a .tga or it wont work...
* Open your program ( i recommend photoshop )
* Do some junk on it...
* Save it as the same name, as a .tga and a window will pop up asking you either 12 , 24 or 32, pick 32.
( if you have problems here tell me )
* Open up image extractor ii ( if it's not already opened )
* Load your edited icon
* Save it as a .blp
WARNING OMG: save it as the same name and put a .blp to the end. Instead of the "Unnamed" write BTNAttack.blp and set quality to wathever u want.
*Open up wc3 world editor and don't close image extractor
*Go to import manager, import your BTNAttack.blp file.
* Right-click on it and open the proprieties window... change the path to...:
ReplaceableTextures\CommandButtons\BTNAttack.blp
ReplaceableTextures is for icons
Commandbuttons is for icons too
BTNAttack is the name of the icon
you can find the filename by going in war3 extractor and type attack, and it will show full pathname of it. if you type ghoul you will see full paths of ghoul related shit.
*Ok... after you changed it to the good pathname, and not war3imported/BTNAttack.blp, save your changes, and close the map, then go test it and it should be there, your new icon.
beceause it overwrited the current one ( only in the map )
i hope you understood, ask me if you didnt..
i also have a good tutorial for skinning, very very detailed