Use an online background remover tool
Upload the image
Let the tool detect the subject automatically
Refine the edges if needed
Download the image with a transparent background
Use Photoshop and select the subject
Invert the selection
Delete the background
Save as PNG to keep transparency
Use GIMP and add an alpha channel
Select the background with the fuzzy select tool
Delete the selected background
Export the image as PNG
Use mobile apps with background removal features
Manually erase the background with a brush tool
Replace the background with a solid color if transparency is not needed