Yes you can up/down grade your account at anypoint
SImply send an email to sales@smpbusinesshosting.co.uk and we will sort it all out for you, and send you an email with the details.
How will it affect my billing?
The only difference that will occur is the price on your invoice and the price you pay, whether it is more or less (dependant on up/down grade). All your login details and login accounts will stay the same