How do I change size of digital pictures in my (save as picture) to fit avatar size?

I took some pictures in my digital camera and apparantly did not see the size.After downloading to my file I want to use some of them as avatars in a discussion site,but I have to change the size.How do I do that.

?How do I change size of digital pictures in my (save as picture) to fit avatar size?
Open them in Paint, change the size and save them (as a new name).How do I change size of digital pictures in my (save as picture) to fit avatar size?
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