I will start by answering your question about changing/removing a credit card.
First, login into your campaign. Under the 4 main tabs, click on 'Accounts & Billing' then click on your 'Account Number' This will bring you to your 'Account Details' and allow you to change your credit card info.
Your other question about Contact Match is I believe it is only in their Beta Program. Most people are being switched over to Beta. If you wish to turn off the Content Match, the instructions from AdCenter guy are as follows:
1. Click the Campaign you want to edit. 2. Click the ad group you wish to modify. 4. Click the Ad Group Settings tab. 4. In the Targeting section, locate "Select a distribution method for this ad group." 5. Uncheck the box labeled “Content” and Click Save.