This Ableton Live tutorial covers two methods for mapping Rack parameters to macro controls. You can engage the Map button at the top of the Rack and click a parameter, then click the Map button under a macro, or right-click any parameter directly and choose a macro from the context menu.
Racks display 8 macros by default, and the Plus and Minus buttons let you scale that view up to 16 or down as needed, keeping your workspace as lean or as flexible as the patch requires.