Janey's quite right; if you keep up with tuning a piano regularly, it doesn't get as bad it probably is right now. When I acquired my piano, it had been neglected for a while, so I had it tuned every six months a few times. But now that it's being played regularly, it's doing much better.
First the tech will want to get the mechanical action all smoothed out (they'll be calling that part regulation), and if it still sounds dead, next would be messing with the hammer felt to fix deformation and hardness changes (that part's called voicing). Voicing in particular is more art than science, and success is a hit or miss proposition, but possibly worth a shot if the sound really bugs you.
There's no point in having the piano if you don't tune it. It's like having a car but putting no gas in it. Usually it should be tuned at least twice a year. A good tuning, from a pretty bad starting point, runs about $80, depending on location. There are professional associations that can put you in touch with a tuner. Just google "piano tuner" or check the yellow pages.
I strongly recommend against doing this. Good way to destroy your piano. Piano tuning is a trade, like carpentry or plumbing. Sure, you can saw a piece of wood in half, but does that mean you can build a house? And tuning a piano involves more than simply tightening/loosening screws.
The brightness is partially affected by the action of the keys (which can be regulated by a piano tuner) and partially by the acoustics of the room. A small room with plaster walls and hardwood floors is going to sound very bright; a piano on shag carpet with many wall coverings is not.
