what are the steps and best practices to upgrade vSphere 4.0 to 5.1?

Hi All,

Currently we have a requirement to upgrade our vSphere from 4.0 to 5.1.

Presently our vSphere consists of:

1. vCenter 4.0 build 258672
2. Its windows 2008 R2 64 bit physical server
3. SQL Server 2008 R2 64 bit physical server
4. 30 ESX hosts running 4.0

Can someone help me in providing the steps to upgrade it and what are the best practices to upgrade it.

Thanks

S.Mani