What fantastic news I am so pleased for you both!
In relation to moving up through the grades you can do so by winning classes - either 1 agility or 3 jumping classes. Up to grade 5 you can progress on points - you get 20 points for an agility win down to 10 for 10th place and 2 for a clear round. In jumping rounds it is 10 points for a first place down to 1 for a clear round. You will need 75 points to progress this way.