QUOTE
Anyways first you need a picture editor like paint, microsoft Photo Editor and Photoshop.(Mine are made in paint and Microsoft Photo Editor)
Select a Picture
Modify it's size/contents
Save as .jpg
Upload the images in the page where you change avatar/siggy
If it's to big in kilobytes go to photoshop and upload them there and then link them
Something more or less like that.
Yoshi you should make a sticky on how to do these things, i've explained like 4 times this.