How do I adjust an actor's speed while in game?

Right now I am trying to find the perfect speed for my game, but I want to test it out in game. I know how to change it, then restart, but what I am looking for is the ability to press “1” to slow the character down and “2” to increase their speed. I have it set up right now so when I push “2” the character increases speed by 600, but no matter how many times I press it again the character does not increase by another 600 which is what I am looking for. Any ideas? So I may learn better can you explain why your idea works so I may better understand the logic and hopefully can apply it else where.

pretty easy to do, you just have to add x value to your speed variable. so event 1 > set “speed variable” to “speed variable” + 600. if you have itt setup like event 1 > set “speed variable” to 600 and thats it, it will just keep setting it to 600, there is nothing to add

Okay cool, will give it a try tomorrow.

This works out exactly as I want it (going to work on when speed < 0 to go backwards, but I will try it on my own before I ask for help), I just want to know if there is an easier way to set this up or if it is in its simplest form.