I want to upload some files to the cloud for storage. I don't want them on my pc as it is memory consuming. If I uncheck sync with local pc, it won't let me do anything to cloud folder. I am using Ubuntu One
There is no way if your pc is linked to Ubuntu 1. The files will keep in sync with your account. However, one way is to unlink your pc and upload the files via U1 web interface.
You can also use one the many free file hosters / sharers / cloud services that allow to continue using U1 from your pc. Assuming the files have a certain size and are useful to you, you will not have much fun with your cloud-exclusive copy. It is better if you keep the stuff local and try to free up some space elsewhere.