To complete upgrade to vSphere 5.1 you need to complete few more steps, depends on design some of the can be skipped.
Recommended:
- Upgrading VMware Tools
- Upgrade the Virtual Hardware for Virtual Machines
- Back Up the vCenter Single Sign On Configuration
- Upgrade datastore files system from VMFS3 to VMFS5
Optional:
- Install or Upgrade vSphere ESXi Dump Collector
- Install or Upgrade vSphere Syslog Collector
- Install or Upgrade vSphere Auto Deploy
- Install or Upgrade VMware vSphere Authentication Proxy
- Back Up the vCenter Single Sign On Configuration
- Join a Linked Mode Group After a vCenter Server Upgrade