First, you need to create a local variable (the name "pushCounter" is arbitrary but just as good as any). That's what the "Create, set or delete local variables" section does in the screenshot above. Then in your rule actions, you can manipulate the value of this variable (so what you're specifically asking about) using Set Mode or Variables, Run Custom Action > Set Variable.
Also, I hate to use this thread to plug yet another custom app I wrote, but Dimmer Button Controller can do this for you without needing to use RM or "track" a variable's value, though RM would give you more power. I wrote it to emulate the behavior of a Hue Dimmer on Hue (with a few optional extra features) if that's what you're after. If you use Hue groups, you'll need to pair it with CoCoHue (or, in general, devices that support startLevelChange and stopLevelChange, which individual Hue bulbs with the stock integration can still do) to get the full effect, otherwise you're stuck with "stepping" up or down by a specific percent on groups. So, one or two options that might help you with this if you're not opposed to custom code or are RM-averse. 
