1. Loosen the string tension by turning the tuning pegs counterclockwise for strings 1 (high E), 2 (B), 5 (A), and 6 (low E).
2. Tune the 5th string (string A) to the note A by adjusting the tuning peg until the string produces the correct pitch when plucked. Use a tuner or reference another instrument in standard tuning to get the correct pitch.
3. Next, tune the 1st string (high E) to the note E by adjusting the tuning peg accordingly. Make sure the 1st string is tuned one octave higher than the open 5th string (A).
4. Tune the 6th string (low E) to the note E, making sure that it is the same pitch as the 1st string (high E), but one octave lower.
5. Tune the 2nd string (B) to the note B by adjusting the tuning peg until it produces the correct pitch, which is one whole tone higher than the 6th string (low E).
6. Finally, tune the 3rd string (G) to the note G, ensuring it is one whole tone higher than the open 2nd string (B).
By following these steps, you can successfully change the guitar's tuning from Drop C (CGCFAD) back to standard tuning (EADGBE). Always use a tuner or reference another instrument in standard tuning to ensure accurate tuning of each string.