iPhone 5 somehow was able to update to 8.4.1 recently from 7.0 now want to update to 9.3.5

[iMore Question]

I don't know how I did it exactly but the used iPhone 5 64gb I bought was at 7.0 and everyone told me I couldn't update to just 7.1 that I'd have to go all the way to 10.1 but somehow after downloading 7.1 ispw file the phone all of a sudden showed on the screen that 8.4.1 was available to be updated to so I did that. Now I want to go to 9.3.5 but can't replicate what I did before to get it to work. I mean I asked for 7.1 and got 8.4.1 but like I said everyone said it was impossible so what did I do? Is this possible? I really don't want to go as far as 10 yet. Thanks. It's an iPhone 5 64gb A1429.