If this is your PC you should be operating under an Administrator's account.
Whose PC is it, as there is always at least one Admin account and it should belong to the owner?
If so then ask that owner to either provide the password for what you want to do, or have them set up an Admin account for you - which must itself be password approved.
What I would do if it is my PC is Clean Reinstall - Factory OEM Windows 7
to set up my own Admin/owner account during install and to get rid of the corrupting Acer bloatware that smothers Windows 7 native perfect performance. If you will stick with the tools and methods given in the blue link tutorial (everything needed is provided) then you will get and keep a perfect install. Save a backup image after setup so you never have to reinstall again.