You can change the label of the available payment methods (PayPal, 2Checkout, Wire Transfer) by going to plugins/system and editing one of the plugins files: rsmembership2co.php, rsmembershippaypal.php or rsmembershipwire.php.
For example, if you want to change the '2Checkout' label to 'Credit Card' you will have to edit the rsmembership2co.php file. First you will need to locate the following line(around line 34):RSMembership::addPlugin('2Checkout', 'rsmembership2co');
..and change the '2Checkout' value with your desired label.
You will also need to set the same label in the following query(around line 106):$this->_db->setQuery("SELECT * FROM #__rsmembership_transactions WHERE `custom`='".$this->_db->getEscaped($custom)."' AND `status`!='completed' AND `gateway`='2Checkout'");