Gifted MacBook running El Captain, need to remove admin

DeeHyder wrote:

A neighbor gave me her old MacBook but has forgotten her Apple ID and password. How can I delete her and use the laptop myself?

Your neighbor must do this: What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

DeeHyder wrote:

The neighbor lost track of her Apple ID and password! So now I don’t know what to do.

If your neighbor lost/forgot their Apple ID password: If you forget your Apple ID password - Apple Support

Your neighbor must take the steps linked to to reset their password then perform the steps necessary to complete before gifting the computer to you.