In case you...
...are still on in the window from where you uploaded the files you will see the list of your confirmed uploads. Here is also a "Delete" button. Use the "Delete" button to remove individual files again.
Even though the file will be removed from the cloud storage, the owner of the CloudWok will see the file's name in his log/upload confirmation, but never the actual file.
...have closed your upload window already, there is no way for us to differnetiate between your uploads and those of others. So you may not delete files anymore once your closed the upload page.
...own a wok and want to remove files form the download tab just access your cloud storage directly and delete the files in there. The download tab only shows a current snapshot of the files in your folder. So removing files from the folder in your cloud will also remove them from the download tab.
(Google Drive - Drive associates also already deleted files currently in the trash with your folder. So you should empty the trash to be sure the files are gone also on the download tab).