Should you upgrade? Only you can answer that question. Having said that, if you're wanting to upgrade simply because the iPhone 7 Plus is a newer device then no, you should not upgrade, in my opinion. Can you upgrade? Of course, you can.
I just moved from a 6s plus to a 7 plus. I made the switch because I changed carriers and needed a new phone but IMO there isn't much difference. I wouldn't spend $$$ on upgrading to the 7/7plus