Translation:I will take the elevator.
"I ride the elevator" should also be accepted. 乗る means to take or ride on transportation.
To use does have it's own verb, being つかう, but のる is being used here. In that sense, to take would be a better English translation because (well me personally) "to ride" isn't used much when talking about an elevator or escalator. Take used in this way also doesn't have a Japanese equivalent as far as I know.
Does using "nori" change depending on whether I'm going up or down the elevator? Could you use "ori?"
Like Yuri said above, "noru" means to ride, not only elevators but cars, buses etc. It doesn't imply any direction. Like "will you take the stairs?/no, I'll take the elevator".
"Oriru", I think, in an elevator context, would tend to the "getting off" sense, rather than the "descend" one (unless duo starts using more kanji).
In natural English maybe, but it wouldn't be a correct translation of のる, which means to ride. The reason why "take" is a possible answer instead of "use" is because "use" has its own verb in this context, being つかう. As far as I know, Japanese has no translation of "take" in this context.