These are the steps to re-string a common acoustic guitar.
Step 1: Necessary Tools
-Wire Snips (optional)
Many pliers have section that can cut strings. It is normally located just above the hinge.
Step 2: Unwind
Using the string tool, unwind each string until it is no longer wrapped around the post.
Notice that the string sound should be lower as the string is loosened.
Step 3: Remove Pins and Strings
Position the end of the string tool around the pin and pull directly up from the bridge. If needed, reach hand through hole of guitar and push pin while pulling from other side. Remove string. Repeat until all strings are removed from guitar.
Step 4: Thread New Strings and Replace Pins
Place circle end of string into the hole from top of guitar. Position pin so that notch faces the hole of the guitar. Push down on pin until it will not go any farther. Test strength of pin by gently tugging on string. If pin comes out, repeat this step and push pin down a little harder than before.
Pushing too hard on the guitar may cause the wood face to crack or break. Gently pushing and tugging on the string is all that is required. Pins will stay in place with relatively little pressure.
Step 5: Wrap and Wind Strings
Thread straight end of string through hole in tuning post. Leave string sufficiently loose, so that it can wrap around tuner post. Bend the string at a 90 degree angle on the other side of the post. Using string tool, wind string ensuring that the bend does not slip back through the hole. Repeat for each string. Snip excess string if needed.
Top three strings should be tightened counter-clockwise and the bottom three should be clockwise.
Step 6: Tune Guitar
Using the tuner, pluck each string and twist tuning knobs until the arrow on the tuner points to O (+-3).
Tuning styles vary depending on the song. Standard tuning, starting from the low E is E(low)ADGBE(high). Dropped D is another popular tuning, where the Low E is dropped to a D; DADGBE(high). Mnemonic to remember string names: Every Average Dog Gets Bones Easily.