Depends on how much you drained to replace the upper. If you only dropped the coolant level enough to be below the outlet you shouldn't have a lot of air to get out.
If you drained a good bit-
I always "finish filling" through both heater hoses. All you need is . . . a funnel! (and a helping wife is a bonus and a win-win) Pull both hoses, and after filling the radiator most of the way, stick a funnel in each hose, in turn, and add coolant (or water) until it just starts to dribble out of the radiator fill. Reinstall the heater hoses to the core nipples.
If it's been a while, the heater hoses will likely be stuck good; I use a hook tool to get in and break loose the stuck hose rubber to nipple, and WD40. If you use the heater hoses to final fill every time they won't get stuck too bad, and it's a good idea to reverse the hoses periodically anyway to help the core from building up blockage crud.
Once it won't take any more coolant, squeeze the upper radiator hose and you'll probably see a few last air bubbles making their way out of the filler neck.
Drive it, check the level after it's cooled off, and top as needed. Don't forget to keep the reservior at the proper level.
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