First, there is "E pi'i i uka". Now, we have "E hele i uka". What is the difference between "pi'i" and "hele"?
piʻi is climb; hele is go
I don't think I've ever heard 'upland' used as an adverb in this way; it sounds rather odd.
Some people say inland or towards the mountains as a translation of i uka.
It's a difference in perspective, like the difference between Cartesian and polar coordinates. It sounds perfectly reasonable for people who live on islands created by volcanos.
It's interestingeaisn't it, how people's perspectives vary due to where they live. Anyway, I agree that it sounds odd at first, but it makes sense.
So both inland or upland could be correct, assuming a mountainous island - right? (But if pi'i vs hele then upland would make better sense?)