Migrating ITMS 7.1SP2 to 7.5 only agents query

Hello,

I have got a task for migrating ITMS7.1 SP2 to 7.5.

I have gone through the procedure of migration.

But i want to know that how all the Agents will be upgraded. Manually or Automatically they will be updated???

And if we want to change the server name then what we will have to do to upgrade from NS..???