One of the more popular SharePoint permissions settings that people look for is to give their users the ability to edit, but not to create or not to delete files. This is understandable as it gives much greater control to the administrators over what users do in the environment, prevents important files from being deleted and the system from becoming bloated with unneeded new files, though some would argue that this restricts the collaborative purpose of software like SharePoint.
The first step to do this is to create a new permission level rather than altering the pre-existing levels in order to prevent confusion amongst people familiar with the SharePoint defaults and also to make reverting to the defaults easier if opinions change. The easier way to do this by copying the existing Contribute permissions level via the “Site permissions” page under the “Users and Permissions” subheading on SharePoint’s Site Settings page. Once there click on “Permission Levels” in the “Manage” section of the command ribbon.
Then select “Contribute”, scroll to the bottom and click on “Copy Permission Level”. On the next page enter the name for this new permission level and a description of it, in my example below I have named the new level Contribute 2.0.
Now in the boxes under “List Permissions” you want to untick the boxes for “Add Items”, “Delete Items” and “Delete Versions”. Now scroll to the bottom of the page and click “Create”, you should now be take back to the Permission Levels page. As an alternative to copying and modifying the existing Contribute permission level you can create a new permission level from scratch, again via the “Site permissions” page, in which case you will choose all the permissions that you want to allow from the start.
Now that your new permission level has been created return to the “Site Permissions” page, tick the box for the user group that you want to change (e.g. Home Members) and then click “Edit User Permissions” in the “Modify” section of the ribbon. On the next page untick the box for the permission level that the group is currently assigned to and tick the box for the newly created level, in this case unticking Contribute and ticking Contribute 2.0. You have now successfully changed the permissions of your members group (or whichever group you chose) to remove the ability for them to delete files or versions and to create new files.
For reasons why the Contribute permission level was used rather than the Edit permission level please see my previous post on Edit vs Contribute permission levels.