Using Actionscript's setInterval(), how can the value of an interval
varialbe change?

In other words, how can the value of [b]intvl[/b] be changed later in the
course of my code?
[i]setInterval(function_name, intvl);[/i]

initially, intvl = 2;
later, intvl = 20;

How can this be done?