The signature policy is probably the most important setting for a Safe Multisig. As it defines how many of the owners will have to accept any interactions with the assets stored on the Safe Multisig or any settings changes. You find your current signature policy under Settings > Policies. In this example, 2 out of the 3 owners are required to send out assets or change the owner structure.
In order to change your signature policy, click on Modify and select the new threshold in the window.
After clicking on Change, your connected wallet will ask you to confirm the change. Depending on your existing signature policy, other owners will have to confirm the change just like a regular transaction.