can tire sizes on truck be changed. My size is 245/70R17 . what to change to 280/70R17?

There is no such size as a 280/70-17. You should not switch to a 285/70-17 as it is 7.2% larger in overall dimeter. You should never go over or under 3% and even then that is not a good fit. You can go to a 265/65-17 if you want a wider tire. It is only 0.19% (.06") larger in overall diameter and is .76" wider and will be a perfect fit.

Yes i would definitely be able to fit, and it would give you more rubber on the road, resulting in more traction. Your wheel base would also get slightly wider and it would give the truck a better stance.

One thing to look out for is clearance issues, so when the tire is mounted turn the wheel all the way to one side and make sure it doesn't rub against anything. For a truck this is highly un likely as there is often all of room.

Yes as long as there is proper clearance left for steering and suspension. All truck manufacturers advise against changing tire specs due to the change in driving and handling dynamics. Your speedometer will also read incorrectly. Check for warranty voids if it is a new truck.