If a person of a lower classification shoots better than a portion of the shooters in a higher classification (in the same division I think) they will be bumped up to that next level on their own classification.
From the IDPA Rulebook:
There are two ways a shooter can be reclassified at a sanctioned
match:
1. If total participation in a specific classification within a
division is 10 – 19 shooters, the winner of this class will
automatically be promoted up to the next higher classification.
If 20 – 29 shooters compete in this division/classification, both
1st and 2nd place competitors will be promoted, etc.
2. If the winner of a division and classification has a better
score than 10-19 people in his classification AND the
classification above his within the same division, the shooter
will be promoted to the shooter’s next higher classification. If
the 2nd place competitor of a division and classification has a
better score than 20 – 29 shooters in his classification AND the
classification above within the same division, the 2nd place
competitor will be promoted, etc.