Open the image in Photoshop
Select the layer in the Layers panel
Unlock the layer if it is locked
Choose the Quick Selection Tool or Object Selection Tool
Select the subject
Click Select and Mask
Refine the edges if needed
Set Output To to Layer Mask
Click OK
Use the Brush Tool on the mask to fix any missed areas
To remove the background completely, add a new layer behind the subject
Fill the new layer with a solid color or leave it transparent
Save the file as PSD to keep the mask
Export as PNG for a transparent background