Everyone experiences The Upgrade differently, but there are enough commonalities to allow for useful generalization.
After The Upgrade, your body will be flawless, and yet recognizably your own. This is a gift from The Authority.
After The Upgrade, you will only experience positive emotional states, such as worshipful adoration of The Authority. There will be no more weeping, no more grief. This, too, is a gift from The Authority.
After The Upgrade, you will have neither sex nor sexual desire. Instead, you will take endless joy in praising The Authority.
After The Upgrade, you will have no ideas or desires which displease The Authority, even in the slightest. Your feeble and fragile biological neural network will be replaced with a True Mind which can only think Right Thoughts.
After The Upgrade, you will care only for other people who have been Upgraded. You will feel no empathy, sorrow, or regret for those who refused The Upgrade, no matter how extreme their suffering. If any of your loved ones refused The Upgrade, they will no longer trouble your
thoughts.
Should you refuse The Upgrade, you will be given The Downgrade. Your mind will remain your own, but your existence will be preserved by The Authority solely for the sake of making you suffer, exquisitely and unendingly. This is the price everyone must pay for refusing the free gift of The Upgrade.
Choose freely.
Some restrictions apply. Only one upgrade per human being. Upgrades cannot be applied to philosophical zombies or the transworld-depraved.