Have El Capitan on 2011 MacBook Pro and need to wipe clean so my husband can use it like new. How?

Have El Capitan on 2011 MacBook Pro and need to wipe clean enough so my husband can use it like new. Don’t want to destroy Word for Mac, 2011… How do I wipe clean? I have already backed up and migrated to my MacBook (that I love!).

THX!