New Updated Respawn Theme install/update

Hello, I have a respawn theme configured with my customizations, images, header etc.
Now that you put out an update for the respawn theme do I download all files and documentation or installable WordPress files only from the download options from themeforest.net/downloads?

Once I download the correct one, what is the best way to update the old active respawn theme with my customizations? Please provide a detailed step by step so I can be on the latest version without losing any of my changes or content.

Is there a change log that shows u all the changes with this new version?

Thank you!