You can assign the folder permissions by following steps.
1.Login to Plesk control panel
2.goto httpdocs folder or your folder path
3.select your folder and click on right side of folder options icon. Select ‘change permissions’ option there.
4. On the next screen, you can see permissions of user, from there you can enable and disable permission rights by click check and uncheck the check boxes.
5. At last click on OK button.