The only correct and best way to resolve an issue of a swollen battery is replacement of the entire battery. The swollen batteries cannot be fixed or healed – just recycled and replaced. Even if your device still works, the battery must be replaced immediately. Using the device or leaving it connected to power can pose risks.
Once a battery starts to swell, it is considered compromised in every way and a replacement is the only way to avoid further damage to your laptop. And most important: At the first sign of battery swelling, back up any crucial data ASAP, discontinue the use of the laptop and discharge it by disconnecting the AC Adapter and letting the battery drain.
Do not press on the swollen battery (or screen or casing that’s popping up).
If your device has a user-removable battery, you can try to carefully remove it and place it in a container in a safe cool place. Be sure to wear eye protection and gloves. Place the device on a flat surface, previously removing all the flammable objects from the vicinity. The laptop should first cool down. Later you could try removing the battery – remember to be careful. Don’t try wedging it up or prodding it with sharp devices, or flex it in a swollen state, and whatever you do, do not puncture the swollen battery—some of the gases could be harmful.
If you’re not 100% sure whether the battery is at fault, you find it hard to remove the battery or are afraid to do it on your own – take your laptop to a service store.