Q: I have a credit in my itunes account but when making a purcahse it is asking for my credit card info.  I don't want it charged to my credit card, I want to use my account credit.  How can I do this?

Hello, Lynne. 

Thank you for visiting Apple Support Communities. 

Here is a helpful article that explains how iTunes purchases are billed. 

iTunes Store: How iTunes Store purchases are billed

http://support.apple.com/kb/HT5582

When using iTunes to purchase content for the first time on a new device, it may require you to verify your payment information as a way to authenticate your device.  If this not a new device attempting to access iTunes store and prompting you provide payment information, there could be an outstanding balance.  This article will show you how to verify you purchase history and invoices. 

iTunes Store & Mac App Store: Seeing your purchase history and order numbers

http://support.apple.com/kb/HT2727

Also, you can change the payment method as none as long as there isn't an outstanding balance on the account.

iTunes Store: Changing account information

http://support.apple.com/kb/ht1918

Hope this helps,

Jason H.