I need to delete apps that I have previously purchased and deleted from my account history
I doubt you can. Your account history is on Apple's servers, so you can only read it. I doubt they'd delete anything from there for you just in case you change your mind and want it back. There's certainly nothing on your computer or iOS device that you can tweak to change your history.
Apple now allows you to Hide purchases using iTunes 10.5. Open iTunes Store > Purchases and then look for the purchases you want to Hide and click the X.
Beware it keeps a list of Hidden Purchases you can still view to get them back.