You can only change ONE letter, AND/OR rearrange the letters currently available. The first word is:
WINS
glow
slow
show
howl
bowl
fowl
wolf
wool
pool
poor
rope
pore
pure
purr
burr
burn
ruby
bury
busy
stub
bust
must
mush
(As when Eskimos tell their dogs to go over soft wet snow.)
much