Original latest navcore is 7.903. TTHome updates in steps, so after 6.520 it should offer you 7.162 (or something) and finally the 7.903 version. You need to disconnect your tomtom from TTHome everytime.
You can also download 7.903 yourself from tomtom and then extract it to your Go.
Download is at
extract to your Go and overwrite existing files (like ttsystem) for the update. When you have rebooted, you are running 7.903.
With 7.903 original you can buy maps from tomtom which are the basic maps without lane guidance or IQ routes info. You can also download these maps and patch them with Easyusetools or yDGPatchter. You also need to patch the Navcore. You can check the maps subforum for the 850 maps compatibility charts.
If you do want more functionality you need navcore SE 8.2** or higher. Best SE version for the Go 500 would be 8.417 or 8.562 since it has limited memory of 32 MB.
Next problem might be that the map you want to use, will not fit on 2 GB. You can use bigger SDHC cards only after your bootloader is at least 5.012. You can download bootloaders from rapidshare and other sources, but I would download it from the source: In a cab from a newer Tomtom, for exemple the xl which comes with bootloader 5.5128:
Be warned that this navcore will not work on your Tomtom since it is not an SE version and is locked to an XL version. You just use the "system" file from it, to update your bootloader. Place the file called system on your tomtom SD card and reboot it. Make sure that your battery is fully loaded and if possible keep your Tomtom on mains power too. It will update the bootloader to 5.5128 and after that you can remove the file system. (It has placed the bootloader in the flash eprom chip). With this bootloader you can read even 32 GB SDHC cards if you want to. Just copy the full contents of your old SD card to the new one.