You will want to modify the user permissions to the folders. If these are local computer user accounts the first thing you want to do is make sure the accounts do not have administrator access on the machine. Then log into the machine as the administrator and modify the permissions on the folders by right-clicking and going to the security tab. Then you can set the permissions for those accounts to something like read/write which will prevent a user from changing or deleting a file/folder.
If this is on a domain you would follow the same process, but you would set the permissions on the file server where the folders reside instead of the local machines. As well best practice would be for you to put all of the users in a group and then assign the folder permissions to the group instead of the individual users.
It all depends on how you have it setup.