The latest version available is MR5 11.0.5002.333.
I would suggest you to migrate directly to MR5.
First you need to upgrade SEP Manager then assign the Mr5 packages to the groups and the clients will automatically upgrade.
However if you want to migrate to Mr4Mp2
then you can do that as well in the same way however
First you will have to migrate to MR4 then again you will have to migrate to MR4Mp2 as per best practises.
Follow the document below on how to migrate to MR5 and how to migrate to Mr4MP2
Migrating to Symantec Endpoint Protection 11.0 RU5
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2009090313483348
Migrating to Symantec Endpoint Protection 11.0.4202 (MR4 MP2)
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2009051906042048