What files should I delete before giving my MacBook to someone else? I am giving my old MacBook to my daughter. I have changed all the names and passwords and so on, and renamed the computer when starting up, so everything seems fine except for the fact that the harddisk must still contain my stuff.

I have erased my self as a user, so I don't show up in finders front window anymore.
Where am I to be found so that I can erase all my files, photos, films and other documents?
Since you are not giving it to some unknown 3d person there is no need to completely erase the drive and reinstall operating system.

You can use the

mdfind in Terminal

for example mdfind user will list all files for the current user

It will even show the deleted files

mdfind user youroldusername 


will show your files if any are left.