Deleting Back-Up sets from Online Storage

I made the mistake of creating a 'Back-Up set' for the whole of my PC, buying more & more Online Storage along the way.

 

Now that I understand the back-up process better, I want to delete this back-up set to free up a large part of the online storage space I have purchased, but despite deleting the back-up sets from within N360 v.5, the available Online Storage space is not increasing. Can I actually reclaim this Online Storage space, or am I stuck with buying yet more space online?

 

Secondly, I read in another Forum post that N360 DOES NOT support incremental back-ups. Does this mean, therefore, that every time I create a new Document/Spreadsheet/picture/music or video file, I will have to create a new back-up set to add it to, rather than simply adding it to an existing back-up set?