An exercise in sed(1) for the interested reader, I'm game ...

sed 's,.*,\L&,; s,.,\u&,; s,[ 0-9][^ ],\U&,g' file
       ^          ^              ^
       |          |              |
       |          |              |
       |          |              Capitalise any non-space char after a
+ space or a numeric
       |          Uppercase the first char
       Lower case the whole name
[download]

echo "
FIRST
SECONF THRID                                                 
RUN4LIFE" | sed 's,.*,\L&,; s,.,\u&,; s,[ 0-9][^ ],\U&,g'

First
Seconf Thrid
Run4Life
[download]