iATKOS | United Kingdom

Hello. My friend gave me his 2009 MacBook Pro that he wasn't using. After some research, I upgraded the RAM and installed an SSD. However, the SSD I installed had Windows installed on it.

When I try to install it now, I can't install it because there is no GUID partition. My Macbook is also very old and won't let me. I don't know how to fix this. Can you help me?