Windows 7: Windows 7 Home Premium OA Restore

Hello, about a year ago I bought a samsung laptop. I want to make a clean install of windows 7. I dont want to restore it on the factory settings because it comes with various other programs that cause some performance issues. I want a fresh windows 7 install. But I have a few questions on how to do that.
What does the OA on the name mean?
If I download the Windows 7 Home Premium iso will I be able to activate it with the key given on the license under the laptop or is the key useless?

Yes you can, good idea as well.

Here is a great tutorial Clean Reinstall - Factory OEM Windows 7

The OA just means it is an OEM system so it cannot be transferred to another computer like a retail license can.

Windows 7 Home Premium - what is this OA in the license tag? Is it - Microsoft Answers

Your Product Key should be good with an legit ISO download.

The license stickered on the machine will be fine for the same Edition of Windows 7 ( any bit version ).

Do you mean COA?

COA and Hologram

I think they mean this OA on the COA sticker,

Yes, its similar to that sticker. I found this site where I can download the iso file: Download Windows 7 ISO (Official 32-bit and 64-bit Direct Download Links) « My Digital Life
Now, if I download Windows 7 Home Premium x64 will I be able to activate it with the product key on the sticker or should I download a different version?

If your PC shipped with Home Premium English, then download Home Premium English. As far as I know the key will work with either 32-bit or 64-bit.