Answer by
LeheckaG (1826)
(1)string-at-a-time!
Turn tuning-post to lower-pitch & loosen-string,
then unthread/unwind old-string.
Straighten new-string and
Re-thread through bridge & turning-post where old-string was,
Kink-string toward headstock's-center.
Tighten, tune, & cut-off excess-string.