Help with resizing pics

How do I re-size pics to add to my signature? I know how to add them to it, but they're way too big.
Also how do I make an Avatar? Sorry to have to ask, but my motto is, "How on earth will you ever know if you don't ask?" Or " The only stupid question is the one not asked" :D
Anyway, any help is appreciated.
Thanks!!!
BTW - I use imagestation if that makes a difference.

Do you have a photo editing programme on your machine - like Photoshop or Photo Editor?

If so, you can PM me and I'll tell you step by step. :)

No Randi, I don't. I do have access to Photoshop, though. I'll load it on my computer, then I'll PM you.
Thank you so much.