ok, SO YOU HAD YOUR CAPS LOCK ON AND TYPED A LOT OF YOUR MESSAGE BEFORE YOU NOTICED. wHAT YOU WANT TO DO IS

Type DAMN CAPS LOC (then we know you didn't mean to shout) OR
highlight it
Use whatever your favorite copy command is (I use ^c)
Paste it into a word processor
Find how to change case, in MSWord it's Format:Change case: and whatever works on the menu

Without need to retype you can get:
Ok, so you had your caps lock on and typed a lot of your message before you noticed. What you want to do is