Tuning a guitar down a half step is a common practice among guitar players for a variety of reasons. When a guitar is tuned down a half step, the strings are easier to bend; less tension allows for faster playing. Some guitars like the "heavier" and somewhat darker sound. This was particularly popular in the 1990s. Another reason may be to accommodate the range of a particular singer.
Use your chromatic tuner to tune your guitar to Eb Ab Db Gb Bb Eb. A normal guitar is tuned E A D G B E. Play your open strings and tune them down one by one until you reach the desired lowered note.
Tune by ear if you don't have a chromatic tuner. Play the sixth fret of your fifth string and tune your low E string to match the fretted note. When in tune, your sixth string should be one octave lower than the sixth fret of the fifth string.
Continue to tune your guitar in the standard way once your low E string is in tune. Fret the fifth string of your low E and match the open fifth string of your guitar to the fretted note. Continue this process up each new string. The only exception to this rule in standard tuning is the B string. To tune the B string, fret the fourth string of the prior string instead of the fifth.
Check your tuning again.
Tuning your guitar down a half step will require more than one pass of tuning for your guitar to completely set in. Tune two or three times, until your guitar is accustomed to the new tuning. Don't be confused when reading sheet music for songs written using the half-step-down method. Music notated for half-step-down tuning is notated as if it is in standard tuning. This is done simply to make note-reading easier. Otherwise, you would be reading a ton of flats and sharps, making sight-reading and analysis much more difficult.
If you plan to use the half-step-down tuning for long periods of time, you may need to adjust the action on your guitar. The different tension may require a different setup than standard tuning. Take your guitar to an experienced guitar repair technician if you are not comfortable adjusting the action on the guitar.