Yes, the "MR" (Minor Release) part number would apply to a 3.1 installation needing to be upgraded to 3.2.
Note that if you have either SAS or SASU contract coverage on your existing license, you should be eligible for a no additional cost upgrade, as opposed to buying it "a la carte".
You can check your coverage by plugging your contract number into the product upgrade tool at http://tools.cisco.com/gct/Upgrade/jsp/productUpgrade.jsp