Are you accessing SEPM using SEPM authentication or AD authentication?.
If SEPM authentication you can excute resetpass.bat
Windows 2003 :
Located under Program Files\Symantec\Symantec Endpoint Protection Manager\Tools\
Windows 2008:
Located under Program Files (x86) \Symantec\Symantec Endpoint Protection Manager\Tools\
Enter User name and password as admin.
You will get prompt to change password.
Note:
Try to excute the resetpass.bat through command prompt as adminstrator if it not works in normal excution.