Use Modify|Remove to schedule the selected files/directory for removal from SVN control.
Select Remove from SVN control and delete locally to schedule the files/directory for removal and to also delete them locally. Select Just remove from SVN control to schedule for removal only. After committing the changes, the files/directories will remain as unversioned.
By default, SmartSVN refuses to remove files or directories that have local modifications, as well as directories that contain modified or unversioned files. Select Force Removal if you wish to perform the removal of such items anyway.