Can I clear out my storage from Adobe Photo Sketch? If I can't how do I purchase more. And how long does storage usually last?
I am not sure what you mean with your storage on Adobe Photoshop Sketch. If you are using the CC storage, it is 20Gb and to clean it up, you have to archive your files and then delete them once they are archived to free some space. There are no chances as far as I know to increase the size if not probably changing your subscription plan, which I would not recommend.
You should be able to draw a huge amount of sketches in the app, but if you are using the storage on the clouds then you have 20Gb and to clear it, archive your pictures or download them to an hard disk if you don't want to loose them, then delete them from the archive.
Hope it helps, let us know!
Additionally, to what Flora just said, If you delete your Sketch projects from Creative Cloud, they will be deleted from your device. In order to store/save them in an editable version, you would want to take them into one of Creative Cloud's desktop apps (Illustrator or Photoshop CC).
Please let us know (either by posting here or through the in-app feedback) if you have any questions about managing your work.