(for rpg maker 2003) "Upgrade" magic system idea help

  While also working on the near death system, I was also going to try a different magic system. Rather than learn newer magic skills and still having the older ones I wanted to try and make it so that they forget the old skill and learn the newer skill. For example, you can let your hero learn Fire, and then at another level learn Fire 2. So you'll have both Fire and Fire 2 skills...

I want to make it so that after using a magic skill a certian number of times it will "upgrade" to the next skill.

Example: After Fire is used 25 times it becomes Fire 2.

So...Anyone have any idea how this can be done? 

Any help or suggestion will be great! Thanks for taking the time to read and post here.

-MasterLink

Use variables. Add one to a variable called...say...FIRE: 0001 every time fire is used and once it reaches 25, change/add the skill. Do this on the monster party screen. I'm not sure how to get specifically fire to level up fire, but for a character to use a certain skill catagory, just click on the "..." and select "Hero uses the _____ command" and add one to a variable.