The service upgrade can be made whenever you like from the Additional Service area of the web site This procedure allows you to increase the space of the database: each 1GB package costs 10 euro (+VAT). 
The Update will have the same duration as the original database. Therefore if the MS Sql is approaching the expiration date first of all you will need to carry out the renewal order and then to make a space upgrade.
ATTENTION: once you have made the service upgrade it will not be possible for you to reduce the database space.