It gets richer with altitude, due to the air being thinner.

Lean it out some.

But not so lean the engine goes pop.

If you like pick a happy medium and then it will sometimes be just a touch lean, and others a touch rich.

My old honda quad gets run from 1,000 feet up to 9,000 feet regularly, its jetted for about 4K to 5K and I leave it there.

 

oh ya and do not forget temps change it to.

 

If your going back and forth I would keep it set for the lowest altitude your riding for any length of time. The reason is lean is dangerous and rich is not, just annoying and you will go through plugs. That's a really big change in altitude and might be worth adjusting back and forth. I used to go up to the mountains outside of Denver and dared not stop the bike, but it doesn't do any harm to the engine.