Hi there. You should try to make the temperature change gradual for them by using heating pads or cooling systems at the beginning. A comfortable temperature for budgies is practically the same for humans (on the warm side) - you can tell if your budgies are cold because they fluff up and stop being as active, and if they are hot because they will separate their wings from their body and "pant" with an open mouth.
You can try the following if they're too hot:
Offer juicy fruits and wet hanging vegetables (like parsley leaves) often, but remove them from the cage after 45 minutes so they don't spoil and grow bacteria.
Offer a bird bath constantly in the cage, but change the water frequently (don't leave too much water in the bird bath; it should be fairly shallow)
Mist your bird with room-temperature water (aim for above the head so that it falls on your bird like rain)
You can use a fan in the room, but don't point it at the budgie or let him get caught in the wind current. This can cause a chill
If your budgie is too cold:
Put an electric heating pad or hot water bottle on one half of the cage with a perch near the heat source.
Cover the cage on 3 sides with a blanket.
I hope this helps! Best of luck