Best way to switch from Windows 7 Enterprise to Professional

[Reanimation]

So recently my main computer had to go in for repairs, so I'm trying to use a spare one.

It's a PC running Windows 7 Enterprise.
I have Windows 7 professional Disc + License etc.

My temporary PC (Win 7 enterprise) has no disc drive and I don't have a bootable usb.

What's the best way Switch OS on this PC?
Should I buy a 7 professional bootable usb pen off Amazon? And use my license? Or will that not work given it's running Enterprise?

Please advise