There are 2 ways to increase your storage space:
By upgrading to any of the paid plans you get additional storage space, HD streaming and multiple parallel downloads.
There are 3 monthly packages:
There are no monthly limits on any of the paid packages, and you can always delete old content to clear space for the new.
There are 2 types of bonuses:
You can get 500 MB for a Twitter post and each friend that signs up with your link, and either 1 GB or 500 MB for a blog post.