Startup disk full vs. emptying the trash

HI. I am having trouble emptying the trash. There are around 3,000 items to remove. I try to securely empty trash, then I get a message saying that some items are locked, not sure how to open them. It's been quite a while since I've used it. And my previous partner used it, so had to tell what was mine and what was hers. I'd really like to clean it up.

I am a photographer, needed to use it to process my recent work. If I can get the trash out, I'd feel more secure about backing the rest of it all up.

Tthank you. Please help!😕

- Adrienne

Have not been able to update iOS yet because of this issue.