I reset my mobile, but it did not delete any files.

brookleeo

Hello, I am Brook, and I have an HTC mobile. I'm facing an issue with my phone. I need to free up some storage, so I tried resetting my mobile. However, I noticed that the reset did not delete any files .
I'm a female driving instructor and rely on storing photos and videos related to driving lessons, which are important for my work. This situation is quite concerning for me. Could someone please guide me on how to resolve this issue? I hope the HTC community can assist me.
Thank you!