Remove the strings from the guitar by loosening the tuning pegs counterclockwise until they are free. Remove the strings from the top peg by pulling them out of the string holes in the tuning peg; you may leave the bottom of the strings attached to the fine-tuners. Write the letter name of the string and the peg that the string was removed from on a piece of paper. This will make it easier to restring the guitar later.
Heat the guitar neck with an iron on a low setting to melt the glue that holds the neck to the guitar backing.
Insert the wooden spatula underneath the guitar neck to separate the neck from the guitar. Using the spatula will help prevent scratching guitar's finish.
Using the steam setting of the iron, place the iron approximately one inch above the neck block and apply steam to the neck block to further melt the glue.
Pull the neck from the guitar by applying pressure to the heel of the guitar. If there is too much resistance, continue heating the neck until the glue has completely melted.
Apply aliphatic resin emulsion adhesive to the sides of the new wider guitar neck and clamp the new neck in place. Allow the instrument to dry for 24 hours before attempting to play.
Restring the top guitar strings by threading one end of the string through the appropriate peg. Use a tuner to check the pitch of each string. Tighten the strings clockwise until the string matches the pitch for each string. You will know if the string is in tune when the needle is in the middle of the tuner. Or, if you have a digital tuner, the display will show the correct pitch.