Hello EK, and welcome to Seven Forums.
It sounds like you may have previously used the SP1 Disk Cleanup Tool
. If so, you will no longer be able to uninstall the SP1.
If the SP1 came already part of the Windows 7 installation in this evaluation copy, then you will not be able to uninstall the SP1.
In Option 2, you needed to open a elevated
command prompt (right click - Run as administrator) instead to run the command in. The link in step 1 of Option 2 can show you more on how to open a elevated command prompt.