Mac OS upgrade

Hi. Can someone give me some advice on what MAC OS I should upgrde to so I can update my LR to the current version? 

I am currently running Sierra 10.12.6. I am paying for my LR/Photoshop and my os is not compatible (am still using the oler version). I dont know very much about this so I am looking for a relatively simple solution here.

Thank you for any help that anyone can provide.