Macbook pro os update not available
I can't get my macbook pro to update the os. It's currently operating n El Capitan 10.11.6. I haven't used it in a little over a year bc i had moved and it was packed in a box in my basement and was having trouble finding it until yesterday. When i go to software update, it keeps telling me there are no updates available.
Is this happening bc it's been so long since last update? How do I get my os to update? I can't use certain apps and things, like Adobe lightroom, bc of my older os. How can i get my os to update?