Updating iPhone 6

I am trying to update the software on my iPhone 6, specifically to 10.2.something. I'm currently running 9.3.4. The reminder to update continuously pops up on my phone 3-4 times a day which is extremely annoying. So after trying to update over wifi, I always get the message that the wifi connection failed and to try again later. The fix on the apple forums is to download the update through iTunes. So this brings me to the next roadblocks. In order to download the current iPhone update, you must download the most recent iTunes version. My iMac is about 8 years old and doesn't meet the requirements to download the most recent version of iTunes. I'm still running snow leopard 10.6 as opposed to the minimum requirement of lion 10.7.

Has anyone else experienced this? Am I forever stuck with these annoying update reminders that I can't do anything about?

I'm also wondering if this is why my battery life will drop from 40% to 1% and then phone dies within a minute.