To upgrade your membership level, please choose the Upgrade link in the member menu or choose any button of advance Subscription other than the current subscription. Your account will be updated/upgraded to that level after a successful payment transaction and then you will be able to access the content allowed under that membership access level.
If you renews/pays for membership before the account is expired, the “Access Starts” time is set to the end of the current term. This applied to “Expire After Access Duration” type of membership levels. So the system basically adds time to the end of the current one. This will ensure that you does not lose any time for the existing term.