Quick question that probably has an easy answer I’m just missing 
Currently, have two monthly membership levels:
Level s2 - $9 Month
Level s3 - $14 Month
If members want to upgrade to level 3, how do I do this without them being charged immediately or more correctly respecting what they have already paid for?
Example: Member joins on April 1st for level s2 and pays $9. After seeing product, they love it and want $14 option. If they click to upgrade on April 1st, are they charged $14 immediately (thus paying $9+$14=$23 for the month)?