Is it a bug or the server delay?

I have been trying to update my banner and blog image for almost a few hours already but those images still haven't changed at all..Is it because the server might take a little time (i've counted now and it has been more than little :| ) to update the picture or is it a bug that i have to upload the image to somehwhere else? I'm still waiting because I have a lot of free time for a few days..but (suddenly remembered i have few exams next week :cry: )