... Change the Render Object's Properties?
The standard render object is a sphere with a radius of 5 units, but of course you do not have to stay with this type of node. Under Render > Render type you will see a list with ready-to-use options. With “Object” you can use any other available geometry:
Create an object or use an existing node.
Drag it to “Render instance” to assign it to the particles.
Avoid high-resolution objects with high particle counts.
Adjust the size by scaling the instance object with Cinema 4D's native tools.
Custom objects will be treated like the built-in types. This means that they can be shaded individually based on their channel data. Please read this page for more information about how to achieve this effect.