I found that the size has to be the same, But Syed Arsalan Hussain is the main Developer and he would know but if it is like most php site the settings for the size would be in one of the css files...ASs far as using a gif file I really don't know...Sorry.

thank you steve, it worked. one question more, i assume you can not change the size or use a gif format? thanks

hmmmm ok ok thk u sir

@ynr nagrohith, try to clear your browser cache.

by using photo shop i edit and upload it and it is asking overwrite and i am saying yes and its complete upload and again showing the same logo sir i am sry

Someone had the same question 6 day's ago and this is what I told them on how I did it.

Yes go to the directory where your ossn files are then go to the directory themes and then directory images and in there your will find logo.png, logo2.png and logoadmin.png those are the three main logo files.

Microsoft paint is what I used to edit them with.