cannot delete photos

i'm trying to clear up memory by deleting old photos and irrelevant stuff. I have some photos which were sent to me

by another person, and i cannot throw them away. i get this message:

" The operation can’t be completed because you don’t have permission to access some of the items."

I went to finder and selected each one and tried to change permissions using my admin password, but the operation was not allowed to complete. many times.

how can i delete these files?