Theme Changing?

Recently I’m working on one of my client E-commerce website but I want to change theme of that website. Can anyone tell me will it effect the ranking of website if I change a theme?

If you don’t use a theme with a slow speed or bad coded one, you should be fine but it’s better not to change the interface like every week.

Just check the new theme speed results, if there’s an improvement compared to your current website, why not?