Progressive Adding To And Removing From

I have a column of data showing trade results - in the most basic way I can explain, as my account value GROWS by a preset amount (say 20-30%) how can I ADD to the number of contracts I am trading. For example I start with $10,000 and the account grows to $12,000 or 20% - according to my own trading rules, this allows me to ADD an additional contract to trade (I start with 1 contract). As the account continues to grow progressively 20% from the previous 20% jump, I add ANOTHER contract.

and to top this off, I do the same in reverse, If I lose or go into a drawdown .. how do I reduce my number of contracts traded?? so lets say I am up to trading 4 contracts and I lose say 10% of the account value - I want to slow down or "ease up" the number of contracts until I get the account back to its previous high. Anyone know how this can be programmed??

One last final caveat - when you go on a winning streak, I add for every 20% INCREASE in the account value and when I lose I reduce contracts at every 10% pullback to preserve winnings as much as possible.but I am ALWAYS allowed to trade a MINIMUM of 1 contract