This means that if you are currently using WhatsApp on a Windows Phone 7, you will be able to continue to use WhatsApp on that phone during this period.
However, as part of this process, after July 1st, 2016 it will not be possible to create a WhatsApp account on a Windows Phone 7 nor move a WhatsApp account to a Windows Phone 7.
It means that only ...
The last version of WP you can install on your Lumia 610 is Windows Phone 7.8.
The exact version is 7.10.8862.144, released the 14th March 2013, as you can see in the WP 7.8 versions history table.
Assuming the download doesn't take too long, the update should take 30-40 minutes.
You are using a Nokia Lumia 610 and WP7.x.
As of the official Windows Phone 7 support page:
Windows Phone 7 has reached end of support, so services and
functionality for this version of Windows will be discontinued over
** Download apps and games FAQ,
You may not have the latest version of the Windows Phone operating
system (OS) on your ...