Got a new phone, want to give my old phone to a family member

Got a new phone, want to give my old phone to a family member.

My new phone is up and running fine. Not sure what to do with my old phone to remove my information.

I thought I only had to change Sim cards but all my data is still in the old phone. What do I do to get my information out of the old phone without harming the information on my new phone?