Retard at the end of a song

Changing the speed of a song

How can I make part of a song slow down as in retard or decelerate? Like at the end of a song.
I am using n-track Studio 24 bit
version 6.1.1

Hi Joe.
Right click in the time axis at the point where you want the tempo change to begin. The dropdown gives you a choice of tempo and bpm change. Also, the little analogue clock icon in the upper right toolbar allows you to choose how speed, bpm and pitch behave.

Smack it in the head with a hammer to make it retard. Do what TonyR says to make it ritard.