The best way I've found is to make a click track that goes along with the song.
Usually the initial tempo of the song will be listed some where, that gets me started.
Their are several tutorials on YouTube on how to find the tempo from scratch.
The best way I have found to find the tempo change is after you have the starting tempo
Follow the song with the metronome. When it gets out of sync go back about 1-2 measures and set a marker then change the tempo following this method.
You will have to play around with a few tempo automations to find out the correct one. Sometimes it changes immediately and sometimes it's gradual.
After you get you automation right, create a midi clip the length of the song using the LC cues. The click track midi will follow the automation.
The other way is to use arrangement view. I'm sure one of the LC guys would do a skype session with you to explain it further.
Hope that helps and doesn't confuse ..,