I will third that recommendation, with this caveat:
I sometimes find that the upgrade guides fail to take a step back to present the various paths. It helps me to have a 10,000 ft view of complex tasks - like looking at a map, before getting turn by turn directions.
Perhaps this is what the OP was asking for?
I do not have such a thing created, or I would post it, but:
1)Upgrade virtual center
a)figure out what to do with the existing db, or ... decide to create a new db. Virtual center is 64 bit only. So you will need to check compatibility of all components of the existing db.
2)Once you decide what to do about VC db, then determine which kind of install to use - simple (where SSO, inventory and VC and the sql DB are installed in one fell swoop on one server) or are you going to spread the pieces out on ore than one server
3)upgrade or install update manager new
4)import esxi image, and create update manager upgrade baseline, apply baseline to hosts
5)remediate using ugrade baseline, one host at a time
There - bare bones, and yes more detail would be nice, but I'm outa time!
PS - I would suggest NOT upgrading to 5.1, as 5.5 will be out soon, and SSO is much improved I hear. I would wait for that, and then wait a month or two, before doing the upgrade. JMO