There are two ways.The fastest way is to simply replace \scp\images\ost-logo.pngAlternatively you could alter the css files to change the file it points to.  \scp\css\scp.cssupgrading will remove either change, but with replacing the file you will have to have the file some where else to restore it... where as the css change you just have to change the path again. 

Very welcome. :)

Can it be any file format such as JPG or does it have to PNG?

If you want to drop a file in and have it work it has to be .png since tha'ts what the css is looking for.If you want to edit the css you can change it to anything.

In /scp/css/scp.cssLine 85:  background(../images/ost-logo.png) top left no-repeat;Line 1506:  background: url(../images/ost-logo.png) center center no-repeat;

forgot to add:  Image file location is in:  scp/images/ost-logo.png

One thing I just noticed:  If I remove the png file completely, the default logo is still there!  Weird?  However, if I issue touch ost-logo.png and create a blank file, the logo will disappear as expected.

i successfully did change logo on Admin/Staff back-end but the logo disappear at Client page. Please help..

nevermind, i thought the clientpage logo file is same with ost-logo.png. sorry but the file was different. it was in assets folder file name logo.png

Correct.  The staff and client ui's are seperate