It's pretty easy as the 2003. Follow the steps in the link below.
http://articles.dashzracing.com/chevy-silverado-2003-2004-2005-2006-diy-tail-lights-installation-chrome-black/
remve the tail light they are on the back side.
The dash light fuse gets its power from the tail light fuse. If the tail light fuse blows, you won't have any dash lights either.
It should if it is the round body style such as 2001 or 2002.
remove tail light and reach through
Remove the tail light housing and replace the bulbs.
Well If you unscrew the taillight from the car take it off you can change you tail light bulbs
From the inside, behind the panels.
you don't replace the tail light you just replace the bulb in it
pull back carpet around the taillight. It should be three plastic caps that unscrew and pull the light out, disconnect the bulbs. Replace with a new tail light.
Read more: http://wiki.answers.com/How_do_you_replace_the_tail_light_in_a_2000_pontiac_sunfire#ixzz1Nur0XSlq
Open the tailgate and look at the sides opposite the tail light sides. There should be two screws. Unscrew them. You should be able to pull the lenses straight out after doing this.
Drop the tail gate down. And look at the side of the bed where the cables go and you will see 2 screews up by the light ,take them out, and remove tail light.