In the Tool Properties view, set the Maximum Size to the desired Eraser size.
NOTE If you are drawing with a mouse, your strokes will always be at their maximum size. If you are using a pressure-sensitive tablet, your strokes will vary in size depending on the pressure of your pen, ranging between 25% to 100% of the maximum size.
In the Stage view, start erasing.
When working in vector, you can also use the Select tool to select drawing objects and delete them instead of erasing.
You can also use Cutter tool to select part of a drawing and then press Delete to erase.