Whilst it might be possible on a 64-bit image by replacing the kernel and device tree files (if you know what you're doing!), we don't recommend it for the majority of users.
Raspberry Pi 5 will require Raspberry Pi OS Bookworm, which will be launched by Raspberry Pi around mid-October.
Once Bookworm is available, use Raspberry Pi imager to burn the image to your MicroSD card, and avoid potential gremlins!
Alternatively, grab an up-to-date pre-imaged MicroSD card here - which will be updated to Bookworm before we ship your Raspberry Pi 5 orders.