Inserting Custom Buttons

Hey, I was makign my map and using hte spell editor, and I wanted to insert custom Button images. How do i do this? Change the file into blp? Just tell me step by step please.

You got to use a file converter or bmp. Extractor.
I got one but im not sure where i got it from but you should be able to get it at any wc3 site.

That's all? Ok I downloaded it, thanks. Easier than I thought.