You can monitor your storage use by using the menu "Administration", "Subscription Status".
It is unlikely that you will exceed the storage allocated to your Visual Pursuits subscription. The storage allocated is generally sufficient to hold 5 years of full size competition images. If you are running out of storage you can reduce your storage use by "releasing" the storage used by full size images.
On one of the Manage Competition pages you can select the "Release Images" button for a competition or Competition Group. This will display a form where you will confirm that you no longer need to store the full size images associated with the competition. The large images will be deleted if they are not referenced in a gallery or another competition. Thumbnail images are retained to help maintain a history of competition entries.