Hi Oleksii,
Welcome to Adobe AEM Community.
In regards to your migration query, on that new AEM Author (6.5.3), will you be creating a Scene 7 or Dynamic Media configuration?
If yes, will it a different Scene 7 account?
As those assets already uploaded on Scene 7, so you may go with moving nodes from one AEM repository to another option.
Thanks,
Vikram Gaur