Consider to replace Sigma 10-20mm F4-5.6 to NIKON 12-24mm F4. is it an upgrade ?

hello,

I have Nikon d7000.  i use SIGMA 10-20mm for landscape and for wide angle photos.I tried to use it for long exposure at night but without much success.

sometimes i think the lens is not that sharp for me. although i took very good photos with the lens. but still i think to do an upgrade to NIKON 12-24mm F4. well, the upgrade will cost about 300$

The question is simple. Is its really an upgrade. i know i will loose 2mm but will i get significantly sharp photos than the sigma in the center and in the corner?

What do you think? is it a real upgrade? how is NIKON 12-24mm in general comparing to Sigma SIGMA 10-20mm.    a specially at 12mm which is better?

remark: I did considered to replace the Sigma to the new Nikon 10-24mm but the cost is to expensive.

Thanks!