Open Paint
Select the Eraser tool
Use the Size option in the toolbar
Choose a larger eraser size from the available presets
Use the keyboard shortcut Ctrl + Plus if supported to zoom in for more precise erasing
On some versions, right-click the eraser and adjust its size from the menu
If using Paint 3D, select the Eraser and change the brush size slider
If the size options are limited, use a larger brush or shape tool with the background color instead