How to Change a UID or GID
The Linux and Unix operating systems use positive integers (numbers) to identify users and groups. The "UID" (User Identifier or User ID) is the number that identifies the user. The "GID" (Group Identifier) is the number that identifies a particular group. A user will have only one UID. Every user will belong to a primary group, but may also belong to multiple secondary groups. The "usermod" command is used to change the UID and GIDs for a single user. The "groupmod" command is used to change the GID for an entire group.
Open a terminal window. The terminal window is found under "System Tools," "Accessories" or "Utilities" in the main menu.
Type the command "su" to switch to the root user.
Type the command "usermod -u
Type the command "usermod -g
Type the command "usermod -G
Type the command "groupmod -g
Type the command "exit" to close the root user session.