Kadence - Content & sidebar widths
Kadence allows you to fine-tune every aspect of your site, and that includes the content width and sidebar width!
Overall Content Width
Go to Appearance > Customize > General > Layout. Under Content Max Width, change the px value to your desired content width. For most sites, somewhere between 1100px and 1400px looks best.
Go to Appearance > Customize > General > Sidebar. Under Sidebar Width, change the % value to your desired sidebar width. If you prefer to set a fixed width (not a percentage), click on the % icon and select px.