To purchase any software title using a credit card or bank account go to the appropriate purchase page. 
A list of purchase pages can be found at:
http://www.caldsoft.co.uk/buy/index.php

 

Select the quantity of licences you wish to purchase, each licence entitles you to install and register the software on one PC. 
Then click on the PayPal button, you don't have to have a paypal account to use this service. 
You will then be asked to log into your paypal account, if you don't wish to use paypal you can pay using a credit card or bank account.   
Simply click on the Continue link, this is highlighted in the image below. 

 

From here you will be able to purchase the software using your credit card. 

The purchase form is shown below.