You can go ahed and for the WiSM upgrade follows the same procedure involved in theupgrade of a 4400 Series Controller. Since a single WiSM module contains two 4400 controllers in it, you need to individually upgrade both WiSM controllers. Also, if you plan to upgrade to version 4 or later, it is recommended to upgrade to the latest version which is version 4.0.217.
For the further information for the Release 5.1.151.0 following URL may help you :
http://www.cisco.com/en/US/docs/wireless/controller/release/notes/crn511510.html