PhoneBurner offers two upgrade options.
To change your account level:
1.Click on My Account in the upper right corner of your phoneburner account.
2. Click on My Account
3. Scroll down to Account and Billing Information
4. Click on Change Account Level
5. Choose either the Unlimited account level or the 7.5 hour account level
In some cases, this may refer you to sales or support for assistance.