Do you think Air France will upgrade me? Long-haul flight?

Of course you can try, but a lot of free upgrades are given to the elite frequent flier members of an airline, so it will be difficult to begin with if you are not one of those.

You can upgrade when you check in (if seats are available and you are willing to purchase the upgrade).

You can dress nice, cross your fingers and pray for a free upgrade. It has happened before!

Nope. All of those empty first/business seats will go to elite frequent fliers a day or two before departure. If there are any left, they will let people pay for an upgrade at check in. You've already bought an economy ticket. Why would they give you more service for the same money? You think on a flight with 100+ people that you're going to be the only one not liking the people around them? If someone is bothering you, the flight attendants will (politely) tell them to shut up.

Unfortunately they won't upgrade you just for asking nicely. Air France, like most other carriers, aren't doing well financially so they will collect you the upgrade fee if they bump you up. Check to see how much it is because their seats in coach class aren't comfy at all. The last time I flew with them, I spent five of 10 hours standing in the galley area because I couldn't take the seats.

Of course they'll bump you up, just not for free. Asking nicely isn't going to get you anywhere. Maybe if you give them proof that your birthday was recently, then they might.

Stick around the desk and when couples are complaining that they aren't sitting together offer up your seat they will either put you in their seat or bump you up, I did this once on some random trip

It's worth a try. Act like a buisness man lol.