It's been about 2 years since I've had my Mac and it's been getting slow lately. So recently I backed up my entire system on an external hard drive and am planning on reformatting this computer. However, when I reformat it I would like to keep it as OS X Mavericks. I've never reformatted a Mac before, so could someone help me with a step-by-step guide on how to reformat my Mac and re-install Mavericks? Thanks.