Don't try to upgrade soldered RAM yourself.

No. This is not a weekend project.

You can technically replace a BGA RAM chip with a higher-capacity one using hot air rework if you have the right equipment and steady hands. But “technically possible” and “feasible for an average user” are very different things.

The problem isn’t just swapping chips. You also need a compatible SPD (Serial Presence Detect) firmware programmed onto the new chip, and the motherboard’s memory controller and BIOS need to support the new capacity. Even if you manage the soldering perfectly, the board may refuse to boot or behave erratically. Many laptops lock RAM training to the factory configuration.

On top of that, BGA rework without a preheater or proper stencil often lifts pads or shorts adjacent balls. One mistake and your motherboard is a paperweight. I have seen experienced repair techs fail at this.

If you need more RAM, buy a device that lets you upgrade it in the first place. This is not where you save a hundred bucks.