On many classical guitars the bridge saddle isn't glued in. If you remove all the strings at once, it can fall out or shift. Changing one string at a time avoids that.
Steps for tie-end strings:
- Detune the old string, then unwind and remove it.
- Thread the new string through the bridge hole from the soundhole side, leaving a few inches out the back.
- Tie it off. Bring the short end back over the top of the bridge, pass it under the main string, then wrap it around itself. Nylon trebles are slippery, so give them an extra wrap or two compared with the wound basses.
- Pull the main string to tighten the knot, keeping the tail on top of the bridge.
- Thread the other end through the hole in the tuning roller, loop it under itself to lock it, and wind it so the string wraps neatly toward the outside of the headstock.
- Tune to pitch and trim the excess, leaving a short tail at each end.
If you'd rather skip the knot, our Classits ball-end sets (SCM101B Medium, SCH102B High) load like a steel-string acoustic. Check that your bridge suits ball-end strings first.
New nylon strings stretch a lot at first, so plan to retune repeatedly over the next several days of playing.