Does anyone know anything about Ukuleles?

Yes changing the strings will make a difference. And it could just be out of tune. Now if you bought one of the little toy ukuleles for about 20 bucks then it will never sound good. And I remember when I first got my ukulele I thought it sounded kind of low too but really ot was just my imagination

Old strings do sound less bright than newer ones. Most guitarists I've known try to change strings regularly--commonly once every 3 months, some do it monthly. There are exceptions tho', I never changed strings until they got so old they could not be tuned, and I understand that Michael Hedges used to do the same--some of us like that darker tone.

But the first thing to do is to tune the thing up to pitch. That may correct your problem. If you search Youtube for ukulele tuning you will find vids like this one:

http://www.youtube.com/watch?v=q-uWfTmAQf4

which should help you.

Back when I fooled around with ukes, I got rid of the stupid pension-peg tuners and put on machine tuners. That makes tuning easier and reduces the likelihood that the strings will slip out of tune while playing. But it's up to you whether you want to pay for those--maybe learn to play it first, decide on upgrades later?

Where did you get it? If you bought the uke from a legitimate music store, they should have checked and tuned the instrument for you before you left. They will still do it if you bring it back to them. If you bought it anywhere else, sorry to break it to you, but it's probably no more than a toy that won't ever sound good.

check if you have tuned it right and the type of string changes the way it sounds

its most likely the tuning, the have free tuners on the internet where you get to tune by ear to sounds coming from the computer

There's not much point indoing anything with it unless you're sure it's tuned correctly.

Try seeing if your uke strings are in the right place because when I first got mine from this cheap place my strings were in the wrong order! And if they are in the right order, try re tuning it with help from a tuner app.