I'm using Ubuntu OS

Hello,

We see you are looking for technical assistance. We request you to start a direct message with us and we will be happy to assist you.

Based on your service tag, the system has an HD display:

391-BCDP : 35.6cm (14.0") HD (1366x768) N on-Touch Anti-Glare LCD with C amera and Mic

Though an external screen may be capable of higher resolution, the internal display panel is not -- the maximum is 1366X768.