One of the best times to upgrade flight is through online check-in, normally 24 to 48 hours beforehand. Airlines will offload excess first- or business-class seats at a discounted price not to have a plane with zero first- or business-class passengers. Check on the web and pick upgrade possibilities—it’s among the easiest means of traveling to a higher class at no extra expense. Gate agents also provide same-day upgrades, particularly if your economy ticket is already reserved. In case you’re polite and hanging around, you will be requested to upgrade seats at an outrageously low fare of what you would have spent.