How to Change the Version of Windows 2008 r2 Standard to Enterprise Without Reinstalling

Useful procedure for changing the product version of windows 2008 r2 standard to enterprise without reinstalling from media.

To determine the installed edition, run:
DISM /online /Get-CurrentEdition

To check the possible target editions, run:
DISM /online /Get-TargetEditions

Finally, to initiate an upgrade, run:
DISM /online /Set-Edition:<edition ID> /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

For example, to upgrade to Enterprise from a downlevel version, run:
DISM /online /Set-Edition:ServerEnterprise /ProductKey:YOUR SETUP KEY

(Thanks to Kimani and Jon)