How to change User Accounts ?
8.1. Firstly power on the mini PC and enter Ubuntu system --> click mouse left key at top right corner of Ubuntu account and choose "System settings..."
8.2. Double click User Accounts --> Unlock.
8.3. Input password --> Authenticate
8.4. Input new User Accounts on the right hand side e.g. PCHD23ubuntu ( On the left hand side My Account is the previous Accounts ubuntu001) --> then click Lock
8.5. Now click mouse left key at top right corner of Ubuntu account, we can see the User Accounts has changed to the PCHD23ubuntu. (the previous Accounts ubuntu001).