The Verizon support page shows that the new software version number for the Lumia 735 is 02171.00002.15194.03084.
Owners of the Lumia 735 can go to the Settings menu, tap Update & security, then Phone update and finally Check for updates to see if the Windows 10 Mobile download is available.
According to the article we Lumia 735 users have to use the Update Advisor to get the W10M update. Just going through the regular phone updater won't get it. I don't know about other devices, but the 735 apparently can only be updated via the Update Advisor application, available in the Windows Store (free).
Like 47seijar said, you need to install the upgrade advisor first, the run it. If the app gives you the OK to upgrade, *then* go to your phones update panel and attempt to update. I did this and it worked on the first try.
The Verizon Wireless support page also instructs the user to use the Update Advisor to get the update. Windows 10 Software Update | Verizon Wireless
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
Follow the directions, you need to get Upgrade Advisor from the Store and run it until complete BEFORE checking for Win 10 via the Update Phone.
Once that is done, then future update will come via the Update option in Settings and will be nearly automatic. Now 10586.420