is the detail engraved into the plastic or raised panel lines out of the plastic?
If it is engraved into the plastic it is fairly easy, sand the joint, watching the panel line, when the line begins to become faint, use an exacto knife with a new sharp blade and scribe along the panel line with the blade at an angle to the surface of the ship... say 45 degrees or so. this will bring it back out... if you sand some more and it begins getting faint again then repeat... Here is an article on it, but you may or may not have all of the tools available... just use what you can to get the panel lines back on your model right!
http://www.swannysmodels.com/Scribing.html
if there are gaps in the seam and this is why you are sanding, make sure you fill them with some type of putty first... there is a good article on it here:
http://www.swannysmodels.com/Seams.html you can't go wrong with the advice on that page.
Note: if model putty is unavailable I have heard people here using CA glue (super glue), wood filler available from the hardware store and a host of other things... be creative! (but always test your filler material on spare sprue from the kit to make sure it will not damage the plastic AND won't be too hard to sand off without sanding the plastic off around it first)
Good luck!!!
---Tom---