Microsoft Paint has several presets for changing the size of the eraser, but you should be aware of the hidden keyboard shortcut that you can use to make an eraser of any size. Unfortunately, this cannot be done on laptops that do not have numeric keyboards. If you still want to increase the size of the eraser, press the keyboard shortcut using the onscreen keyboard.
Steps

Step 1. Select the Eraser in Paint
The eraser can be selected from the Home tab. For this to work, Paint must remain active.

Step 2. Click on the "Thickness" button to select one of the available sizes
This button is on the Home tab, to the left of the Color Picker. If these sizes do not suit you, press the + sign on the numeric keypad to change the size.

Step 3. Open the onscreen keyboard
Typically, the eraser can be resized using the numeric keypad by pressing Ctrl ++ / -. If your laptop does not have a numeric keypad, use the onscreen keyboard, which simulates a full-size keyboard.
- To open the onscreen keyboard, click the Start button and type the word keyboard. Select On-Screen Keyboard from the search results.
- Note that the onscreen keyboard remains visible even when Paint becomes the active window.

Step 4. Click on the "Options" button on the on-screen keyboard
By default, the onscreen keyboard does not have the numeric keypad enabled. It can be enabled in the Options menu.

Step 5. Check the box next to Enable Numeric Keypad and click OK
A numeric keypad appears to the right of the on-screen keyboard.

Step 6. Hold down the "Ctrl" key and then click on the "+" sign on the numeric keypad
You will notice that the "Ctrl" key will remain selected until you click on the "+". Press the "+" sign on the numeric keypad, not the one next to the "Backspace" key.

Step 7. Continue pressing the "Ctrl" and "+" key until the eraser becomes larger
Each time you press these two keys, the eraser will grow by one pixel. In other words, you will have to press these keys several times before you notice an increase in the size of the eraser. Try pressing Ctrl and the + sign 10 times to see the difference.
- If the eraser does not resize, make sure Paint remains the active window when resizing.
- To reduce the size of the eraser by one pixel, follow the same steps with the “-” sign on the numeric keypad,.
- You will have to press the "Ctrl" key before each press on the "+" or "-" signs.