If you are upgrading to a hosting plan that has a higher monthly cost than the one you are currently using, you will be charged the difference in price between what you have already paid and the cost of the new type of hosting purchased for the same period of time. If you downgrade your hosting package a request must be made in order to receive a refund for the difference in cost.
If you are intending on using ASP or .Net technologies you should use a Windows hosting account. Similarly if you are using PHP/CGI/Java/Perl in your sites you will need to use a Linux based hosting account.