In File Manager, select the icon of the file or folder whose mask you want to modify.
Choose Properties from the File Manager Selected menu or from the icon's pop-up menu (displayed by pressing Shift+F10 or mouse button 3).
The Permissions dialog box appears.
Click the Show Access Control List button if the folder has no ACL defined.
If the folder has an ACL defined, it will be visible when you open the Permissions dialog box.
Select the Mask entry in the Access Control List Permissions scrolling list.
The current mask permissions appear in the Effective column.
Click the Change button.
Click the Permission check boxes to reflect the values you want for the mask.
Click the Change button in the Change Access List Entry dialog box.
Use the Apply Changes To option button to choose the scope of the permissions changes.
For files, the options are This File Only (default), All Files in Parent Folder, and All Files in Parent Folder and its Subfolders. For folders, the options are This folder only (default) and This folder and its Subfolders.
Click OK to apply the current settings and dismiss the dialog box. Click Apply to apply the settings without dismissing the dialog box.