Silly question but how the hell can I make my avatar picture big like other people?

If you're using attachments, don't use them. Attachments shrink down pictures to ridiculous sizes.
Either upload your avatar to another site such as imgur, or just upload it directly from your computer.

Just change the resolution to the maximum possible for the forum, it was 100-100 for Profile Pictures and avatars 185-185 or something like that.Simply put it in Photoshop or paint or whatever programme for picture editing you have and resize it to the resolution you want.