you are making me jealous!, i have not bought trousers for years and now have a pair of linen ones but need to turn them up easy i thougth but now am trying to do it but not sure how and cant afford to send them to the dry cleaners.
If they are at all flared you will need to unpick the side seam a little way and then open it up v shaped before turning up and hemming. Use stitches that catch a single thrad of the material each time so it does not show through.
It depends on the type of trousers. I ahve just bought a pair of linen ones too which are a bit too long. they are fairly baggy tho not tailored so makes it easier. Id go for had sewing rather than machining as its mush easier to adjust as you go along or use wonder web as suggested here its fab stuff.
I think it depends on how much you need to turn them up (do you need to cut them) and also do the trousers taper in or out at the bottom (if out then its easy just add a tuck in the hem, if in then much tricker as you may need to undo the hem at the side a bit)