BabemRoze

Best answer as chosen by Asker / Ratings
Heya :3
I was stuck on this too only a few minutes ago but here's what you do. After reading the books in the library you should be able to perform these paces. But it's not as easy as you may think. To do the other paces you need to:

Extended Walk: Go into walk and press L
Extended Trot: Go into Trot and press L
Extended Gallop: Go into Gallop and press L
Collected Walk: Go into walk and press R
Collected Trot: Go into trot and press R
Collected Gallop: Go into Gallop and press R

And here are other things I assume will arise further in the game:

Passage: Go into walk and press P
Pirouette at a walk: Go into walk and press T
Pirouette: Go into trot, working canter, or gallop and press T
Flying change of leg: Go into trot, working canter, or gallop and press C
Half pass at gallop: Go into gallop and press A
Shoulder in: Go into trot, working canter, or gallop and press E

Thats all it is ^_^

If you need more info there's a manuel on the CD just go to "My computer - CD - Right click - Open - Support - Manual - Manuel" Thats where I found what to do lol :P

And it's all there ^^

I hope this was helpful :D
Good luck!
BabemRoze