Wifi networks are very convenient. They are especially convenient for cyber criminals when they contain important resources and aren't secured with a strong password.
There are two approaches to dealing with Wifi security.
Secure the Wifi
Set a strong Wifi password for any networks that have your business systems and information on them. Wifi passwords only need to be setup once per device.
Change the password when someone that knows it leaves the business. If that's not practical due to turnover, change it at least every three months, or better, use a system where staff individually log on to the wireless network so you can remove this access when they finish up.
If you provide a guest Wifi network for visitors and customers, make sure this network isn't connected to your business systems, but goes direct to the internet. Your service provider or IT person should be able to help.
Treat the Wifi network as the Internet
If you don't have any local systems or services on the network, you can simply treat the Wifi network as untrusted.
For example, if all your laptops use cloud services and there is no local IT resources, you don't need to worry so much about changing the Wifi password. It still doesn't hurt to set a decent password, if only to stop people stealing your internet access and running up big downloads.