When you mention a "database on the network" (and mentioned your OS), I hope you mean a database available on your Lotus Domino server. Lotus Notes is not a peer-to-peer application and requires a Domino server to enable multiple users to access a database synchronously (at the same time). If your database is simply stored on a network share, only one user will be able to access that application at any one time.
To modify the ACL you will also need to open the database using an ID (username) that has at least "manager" access to the database.
To change the ACL:
- Open the database.
- From the menu, choose "File" -> "Database" -> "Access Control."
- Under the "Access Control List" section, click the [Add] button.
- Choose the name of the user/group that you wish to grant access.
- From the "Attributes" on the right hand side of the ACL dialog, change the "Access" for the user/group you have added to "Editor."
- Choose the [OK] button in the ACL dialog box.