Switching to new system images will give you access to newer versions of Python. It will also change the versions of packages that are installed in your environment. You can check what packages are installed in which system image here.
If you would like to upgrade your system image for your PythonAnywhere account, you will need to contact an administrator by pressing "Send feedback" on the dashboard.
Switching to a new system image may break your code that was working on your old image. You will also need to rebuild any virtual environments you have created.