Hello Tammy,
If within the credits system you have set that user will receives credits for certain action, it doesn't really matter which user role user is subscribed to. He will receive credits for that action regardless of the user role.
1. to receive credits for any actions, this action needs to be disallowed in user roles. For example for "free" user role you have unchecked the box for "Add blog". Within credits you have set "+5" for "Add blog". So user comes, registers >> gets default free user role >> posts 10 blogs >> gets 50 credits.
2. since you have already set that for adding blogs user will receive "+5" credits, you can't change this setting for particular user role only. If user subscribes to "advertiser" user role he, just like the free user, will receive 5 credits for adding blogs. He can't loose 5 credits, he can only receive them.
3.At the same time you have decided that for "Adding groups" users should loose 5 credits. So free user role user comes >> adds group>> loses 5 credits ( gained for posting a blog).
Advertiser role user comes >> adds groups >> looses 5 credits ( gained for posting a blog).
What I would like to say here, is that your advertiser user doesn't really need to upgrade to gain those credits. He can get them using his own role.
If you provide more information on exact set up on your site, I might help you more, since it is now very difficult to image the situation you have described and may be I just understood you in a wrong way. Can you provide more info on :
1. User roles you have and their permissions for certain actions ( take only 2 as example)
2. User credits settings for selected 2 actions.
3. What happens with users subscribed to your different roles when they try to complete specified actions.