Expanding on Gary's answer, the following was done in Adobe Photoshop CC 2018 on a Mac. For this to work as expected, please ensure your subject is on a separate layer from your background. Also, make a duplicate of your subject layer before starting, just in case.
Select your subject by holding Cmd(⌘) and clicking on the thumbnail of your subject layer. A dotted line outlining your subject will appear. Go to your taskbar at the top of your screen, click "Select", scroll down and click the "Select and Mask" item, a Properties tab will appear on the right.
Under "Edge Detection" change the radius pixels to an amount you deem sufficient. If you require further refinement, you can play around with the "Global Refinements" options.
After modifications are made, select "Ok" at the bottom of the tab. The dotted line will still be around your subject. Press Cmd + Shift + I to invert your selection, press "Delete". Your edge should now be deleted to the pixel amount you specified in the "Select and Mask" screen.
Alternatively, you can modify your subject's edge selection by clicking Select > Modify > Contract in your taskbar. Once you have input the number of pixels you wish to contract, select the inverse, and hit delete. Voila.