Sig and Avi help please!! (resizing pictures)

Hello fellow Fark board posters. I unfortunately am very illiterate when it comes to pictures and sizes and what not so I am here to ask you for help..

I would like this picture.. (already my avi but small) to be resized to the biggest size avi pic that still follows the rules of the website..




And.. I would also like some help resizing this picture for my signature.. Again.. to the biggest size possible that is still within the restraints of the rules of TD!




Please and thank you!!