Replying to Trouble Changing My Icon

so my friend, vt_scratch gave me an icon, the K2 one, a while back and i want to change it. but when i click on my icon to edit it and try to upload a 50x 50 pixel icon, my icon does not change, and it says that the icon must be 50x 50 pixels even though the pic i uploaded was 50x 50. my question is if anyone knows how to upload icons correctly and if i am doing something wrong? also its not my computer thats the problem either cuz my friend tried to change it at his house too but it didnt work. +k