You can "rescale" your system, even after starting it, but only in the downward direction. (For example, if you start your C2 system with $100,000 in hypothetical cash, but decide you'd rather trade a system with $10,000 cash, you can rescale. You can't give yourself more cash, however.)
To rescale, go to your system detail page, click on the Manage button, then Rescale as in the picture below.
Your strategy must be flat (no open positions) in order for a Rescale to occur.
To attract the greatest number of subscribers possible (and to make AutoTrading simple and easier to control for these subscribers) your system should have the smallest amount of capital as is feasible for your trading method (leave room for the inevitable drawdown, of course). When you have a lot of "extra," unused capital in your system, you make it more difficult to AutoTrade your system and scare away subscribers.
IMPORTANT NOTE: Rescaling is much like stock splits. The idea is analogous to what happens when a stock split occurs: the historical price charts for the stock are changed to be consistent with the new per-share price.