How do you save the level-ups to Skylanders Giants figurines?

Started playing Skylanders Giants last night and leveled up to Level 3 on Tree Rex. However, when we switched to 1 player on the same story line instead of 2, and went back to the first world/level to get items we had missed, it dropped back to Level 1 instead of Level 3. Could have been because we switched out characters as well. Is there a way to hard save to the figurine what you have done with it? Haven't been able to find the controls to do so. It's a Wii Portal, if that makes a difference. Thanks!