your best bet would be to back up all your data and do a clean install with the most recent oem version of 7600.that way will be asier to activate with the activators posted here.also a clean install will take less time and increase the quality of the system.hope this helps.
But you can also upgrade! in the build 7600 ios there is a file named cversion.ini open it with notepad and it should be something like this... [HostBuild] MinClient=7233.0 MinServer=7100.0 change MinClient to 7000.0 and save. rebuild the iso and burn.