I am sure you could replace it yourself but don't you have any warranty on your phone or insurance? After all it is only a week old. Instructions are here [[Device:HTC Evo 4G#deviceGuides]] and the parts you are looking for are here as well as my favorite store :) www.ebay.com
http://www.repairsuniverse.com/htc-evo-4g-screen-replacement-repair-parts.html hope this helps :) good luck