How to upgrade hard drive in Mac Mini I recently bought a new mac mini (my first mac ever yay) with a 1TB hard drive at 5,400 rpm. the guy at microcenter also sold me a 1TB hard drive at 7,200 rpm and said it shouldn't be to hard to replace. He said first I'd need to back up the OS to a usb thumb drive and then physically replace the hard drive and then some how get the OS onto the new hard drive. 

So far I've found a few tutorials online on how to physically replace the hard drive but it seems like a lot more work than I anticipated (ie. http://www.ifixit.com/Guide/Installing+Mac+Mini+Late+2012+Hard+Drive+Replacement/11716/1). Although, it does seem like something I could do.

However, my main difficulty now is i'm having a very hard time finding any help online on how to 'back the OS up on a usb thumb drive' and how I should re-install it once I do put in the new hard drive. He mentioned using time machine but when I open time machine it doesn't give me any options to interact with the USB thumb drive.
I recently did this very thing. I backed up my OS and files to an external drive (not a thumb drive), installed the new drive with new OS, and restored the Time Machine backup to the new drive. The whole process took a couple of hours. The best online video for doing this operation IMO is here: http://eshop.macsales.com/installvideos/mac_mini2011_hd/
Replacing the hard drive will not void your AppleCare warranty. OWC addresses this issue on their blog: http://blog.macsales.com/18244-owc-diys-wont-void-your-macs-warranty


NOTE: I have done the restore process in #1 using both Time Machine and Carbon Copy Cloner. Each is different, but relatively simple.