I recently got a notice that there was a software update available for my Windows phone. Since I was about to head out for some camping with the family, I was not able to do it. In fact, I only wanted to enjoy some nature so I didn't use any technology ;>
The notification disappeared. I believe it will periodically notify, but I am not sure of the schedule. So, I had to manually force the update by going into the Settings, then "phone update". I selected both options already - "Tell me when updates are available for my phone" and "Automatically download updates if my settings allow it" [in other words, you likely need to be on WiFi].
I went into Show Details, read the notice and hit Install.
Piece of cake!