You would accelerate, then at the halfway point (astrogation on ship's computer will total and do this - the crew will be in Grav-couches for the trip) you deccelerate at the same rate. A set of gravity drives in the ship would get rid of the remass problem (you'd still need some fuel to power it -keeping it turned on- though).
We're talking about a level of technology that is very advanced and doesnt work like our currently decommisioned space shuttles did - it would be faster and way more efficient.
I only mention this as this would be how time dilation would factor into the plot in its actual way - and thats if the destination is Zeta 2 Reticuli and the ship doesnt end up drifting to it or whatever planet the ship will land on. As I work out all this hard scifi information, the less I see the film doing something like this - though maybe someone can pick this up for an Alien fanfic, eh?