alright, I'll explain it in full:
you can only couch Lances now, and there are now 2 ways to couch:
Manual and Automatic.
this setting can be found in the Gameplay tab in the Options menu. Manual makes you press 'X' (or whatever you have set to change how a weapon attacks) whenever you want to couch, and lasts only a few seconds.
Automatic is basically the same as in the original M&B, except you can still only couch lances.