You usually have to unbolt the rail, and you may have to disconnect the feed and return lines. Once th rail is free, you pull it up and out, and then you remove the injector(s) from the rail. You can relieve the pressure in the rail by opening fuel filler cap and letting it sit for a while. You can also loosen the the feed line slowly. There will invariable be a bit of fuel left in the system, so strategic placement of paper towels is recommended, as is disconnecting the battery and resisting the urge to light up a smoke.