I want to upload all my pictures, videos and documents to Ubuntu One and then delete them off my pc and forget about them.
Is this possible?
You can use the "Disconnect" button ("Desconectar" in spanish) in your Ubuntu One's client top right corner, after which your computer will stop syncing until you click it back to re-connect and this way start syncing again. You can also stop individual folders from being synced and re-synced again by simply activate/deactivate the corresponding checkbox in the same window.
Both options allow you to run a first time/one time sync and stop syncing, so you can delete what you don't wish to be in sync and it will remain on the cloud but if you reactivate the global/partial sync, the files will come to your computer.
Here is a screenshot (This system is in spanish, just for your consideration)
The solution I can think of is to upload your photos and then uninstall Ubuntu One from your PC.
This way, your PC won't be syncing, but your photos will remain "in the cloud".