Yes, you can do so.
Just note that you will have downgraded to the Starter edition then, losing all Business edition features. So, certain things you have been using before may not work anymore, and the settings in the configuration will not be available any longer.
As always before significant changes such as up/downgrades, I guess you want to make a full, restorable backup of your site including database.
See here for feature comparison, meaning what you'll lose:
www.hikashop.com/extensions/compare-versions.html