Will changing my Apple ID affect any apps that I have purchased?
If you have an Apple ID that ends with mac.com or me.com then you probably can't, otherwise this FAQ covers how to change your Apple ID.


Go to http://appleid.apple.com/
Click "Manager your Account"
Login to your account
Click on the "Name, ID, and Email Address" option on the left
Next to Apple ID click the Edit button and fill out your new details.


Purchases are bound to your account, so short of deleting your account you should be fine. (In fact you can still access old purchases by logging into the relevant store with your old account according to the FAQ about Apple ID