Ugh..HELP

This is kind of a stupid question but I'm not very smart with computers...anyways how can you change the format of a picture because I'm trying to put a picture of me on here and it keeps telling me that it's not in the correct format and it's really pissing me off lol..so can you help please!

Problem Resolved!!

Hahha lol i wish i knew how to put a picture of me up:) i just dont know how??