My Heroic membership expires in about a week. Rather than letting it auto-renew, I'd like to start paying for the Master level. Is there a way to do this upgrade without losing the scores of characters I've created? I assume if I turn off auto-renew on my subscription, then sign up for Master, I would achieve my membership goals. However, in the small downtime between the two memberships, will all but 6 of my characters be erased? Surely there's a way... Thanks in advance. 

Edit (based on posts below): you will probably only be able to access 6 of them, but access to the others will be restored when you re-subscribe. They will not be deleted.

Should a subscription lapse while you have more than 6 characters, you do not lose access to any of the extras. You can still edit and level them, but the character count should say something like 35 / 6 characters instead of 35 / unlimited. If you ever delete a character, it will change to 34 / 6. You will not be able to create any new characters while over the limit.

In short, we won't lose any of your character in that transition time, you just can access only 6 of them. The access to all the characters will be restored at the activation of the new subscription.

I don't think you can edit your extra characters.  It used to be the case that if a subscription lapsed, you would be asked which 6 you wanted to continue to have access to, and the others would be locked.   But once a subscription renewed (of either type), access to those locked characters would be renewed.

Great! Thanks folks!