Yes. Just delete .svn folder and your folder will no longer be under the control of subversion.
The .svn folder is the pristine copy of your repository when you did the checkout. So, it acts as the link between your server and your working copy. Once you delete it, you lose this "link".
Edit:
If you have any subfolder in your project, you will have a .svn folder in each of them. So, if you want to remove the link to subversion, you need to delete these .svn subfolders.