The easiest way I found is to do the following:

1. enter non-admin powershell (by just typing powershell at the command prompt)
2. type: runas /user:admin username powershell
3. enter the appropriate password when prompted

You're done!

An alternative method is to do the following:

1. type: runas /user:admin username powershell
2. enter the appropriate password when prompted

You're done!