Currently, Keepsafe does not actually have a 'log out' option. In order to log out of your Keepsafe account, you must uninstall your Keepsafe app.
NOT recommended: Any unsynced content will be permanently lost in the process.
If you still intend to do so, make sure that all of your items are backed up before uninstalling the app. Only the backed up content will be restored when you log back into your Keepsafe account.