hello anybody. how can I upgrade my Mac book air up to 16gb if I may?

Only 2018 and later MacBook Air models can be configured at purchase with 16 GB.

It's very easy to determine if your Mac's performance is being limited by available memory. Please read Check if your Mac needs more RAM in Activity Monitor - Apple Support. If the "Memory Pressure" graph is frequently "red" your Mac would benefit from additional memory. If not, it won't. It's that simple.

No MacBook Air has memory slots so upgrading the RAM is not possible.

The last 11 " MBA from 2015 according to this site https://everymac.com/systems/apple/macbook-air/specs/macbook-air-core-i7-2.2-11-early-2015-specs.html

There have been 21 MacBook Air models, 6 are 11" models, and as I mentioned in my post, you can't increase the RAM with any of them.