How do I change the models of characters that already exist in the game?

To do this, you need to replace the configuration files. You need to find the main files for the angel and black knight (in .xdb format, which can be edited with Notepad) and work from there. These files are located in data.pak in the data folder. This archive can be opened with any archiver. You can find the necessary files there.

Which specific files? Everything you wrote, I already knew, and I've opened the xdb files and data, and I even managed to create retextures (and don't think I'm ungrateful, thank you for explaining to those who don't know), however, I haven't figured out how to change the models themselves. I thought I needed to change the paths in gameMechanics-creaters-haven-angels, but it didn't work.