Heh, I can shift gears all right, but I hate hills anyway. Here are a few helpful(?) tips:

Shift down...

If you want to fight the hill, you can stand on the pedals, but that might not even be faster when big hills are concerned, because you'll tire yourself. Gear down so you can maintain your cadence.

...but not too far down!

If you select a gear that's too low, you're just going to lose momentum and end up going slowly with just as much effort as going a little faster would have been.

Shift early...

If you wait too long to shift, you won't be able to do it smoothly: the chain will jump from cog to cog sharply, causing you to lose momentum and maybe even balance. Or it might just refuse to shift altogether. Anticipate when the pedalling at the given gear is going to get too difficult, and shift just before then.

...but not too early!

If you shift down too early, you'll end up losing momentum and gaining nothing.

Pedal in circles

It's harder to pedal in circles going uphill than at other times, because the pedals don't have as much momentum to carry over the "dead" point (pedals at 12 and 6 o'clock). If you find it absolutely impossible to do circles, and have to mash the pedals down, that's a hint that you're trying to do it in too high a gear (unless the hill is really steep ). It's not going to be "perfect" cirles - a hill pretty much always means you will probably deviate from your normal technique towards a bit more mashing, but the difference shouldn't be extreme.

Just for an experiment, pick a long hill, put the bike in an easiest gear that you have and ride up the hill in that gear, not worrying about how long it takes. It will take you forever, and you might wobble a little bit even (due to such low gear/speed), but it's not going to be exhausting at all. Then try the same hill again in a somewhat higher gear, until you find a comfortable balance between speed and level of exertion.