You have to be careful here--if you take too much, the pants will not lay correctly. If there are no side pockets, and no lining, you should be able to take them up the side seam.....don't do the inseam unless the crotch is also hanging too low. If the pants fit in the hips and waist and just the legs are too big, you'll need to fade the seam in around the hip area....and it needs to be gradual so you don't get a pucker.
Unless you are an accomplished seamstress, I'd recommend taking them to a tailor to have them altered. Now, if the pants aren't that expensive, and you want to experiment, go for it!
Kim