Lubuntu resolution 1920

Open a Terminal by CTRL+ALT+T

Type xrandr and ENTER

Note the display name usually VGA-1 or HDMI-1 or DP-1

Type cvt 1920 1080 (to get the --newmode args for the next step) and ENTER

Type sudo xrandr --newmode "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync and ENTER

Type sudo xrandr --addmode VGA-1 "1920x1080_60.00" and ENTER (replace VGA-1 with your display type (step 3) like HDMI-1 or DP-1)

Now close the terminal and go to Settings >> Display settings and change it to 1920x1080

Enjoy FHD.