Hi vamsi,
Please check following KBAs about how to change the logo. If you still encounter problem, please provide me the information in more detail. A screenshot will be appreciated.
1.how to exchange logo in WebUI without skin copy by using customize node "Define http://service.sap.com/sap/support/notes/1849835
2. Missing customize node "Define Icons" at IMG
http://service.sap.com/sap/support/notes/1713658
Best Regards,
Brcue