After accidentally logging in with a Microsoft account on my Windows 10 PC, the local account profile picture has been set to that Microsoft account's profile picture and I didn't see an obvious way to change it. Now I figured out where the settings are and how to remove old profile pics that you no longer want.
Change Local Account Profile Pic:
Start Menu -- Settings -- Accounts -- Your info -- Under "Create your picture" -- Select your new pic.
Delete old ones that you no longer need:
Open Explorer -- Put "%appdata%\Microsoft\Windows\AccountPictures" (without quotation marks) in the address bar -- Delete pics that you no longer want.