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.
If you wish to get additional storage for free, go to Get Space, or get more information at How to: Get More Space.
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.