Runtime environments for individual function instances

Hi folks, Very much a new user of the AWS environment.

We have a few functions in Lambda each currently running the soon to be depreciated Node.js 12.x for it's runtime environment.

I am looking to update Node.js for one of the functions to test it, but I wanted to check whether updating the environment in one function will only effect it's instance and not all of the functions I have created?

Has anyone done this previously that can confirm this?

Thanks in advance.