Instructions
Confer with your group's Game Master to go over the rules of the game and discuss any important changes that would keep your character from remaining as it is.
Define your character. Remember that your character was a "character" because you endowed him or her with certain personality traits and special quirks that set them apart from other characters. Ask yourself questions about your character's personality traits, playstyle, combat style and overall demeanor. All of these questions are key to capturing the spirit of your character and transferring it to 4th Edition.
Check that your character's race and class are still available. Certain races(gnome, in particular) and certain classes(like the monk and the barbarian) have been removed from the basic Player's Handbook. You need special permission from your Game Master to continue with these races.
Compare your character's personality, playstyle and role in the group to one of the 4th edition character templates: Striker, Leader, Controller or Defender. Refine your character's new role if you want by choosing "class build," located in the "Creating A Class" section in Chapter 4 of the 4th edition Handbook. There is always the option to choose a predetermined class, but those classes may not have the correct combination of feats, skills, and other powers that your character possesses.
Check what level your character is. If your character has gotten high enough to specialize into a prestige class in 3rd Edition, consult with the Game Master about which prestige classes are available to you in 4th Edition.
Complete the process by filling out your character sheet with the appropriate information. If you get lost, ask your Game Master or a fellow player for help.