I bought a Lenovo Z50-70 few days ago. I'm trying to set full HD resolution 1920x1080, but the maximum available is 1366x768. This laptop reportedly has a full HD screen. Graphic card drivers are the newest possible.
You may have inadvertently purchased the HD model with a max resolution of 1366x768.
According to the specifications, the HD model has a resolution of 1366x768, and the FHD has a specification of 1920x1080.
Some: 15.6" (396.2mm) HD (1366x768) color, LED backlight, 16:9 aspect ratio, 200 nits, 400:1 contrast ratio
Some: 15.6" (396.2mm) FHD (1920x1080) color, LED backlight, 16:9 aspect ratio, 200 nits, 400:1 contrast ratio