In Salesforce, each opportunity stage will have a probability and forecast category assigned to it.
In order to update the probability or forecast category, see this video or follow the steps below:
Open your Funnel editor to a Canvas with an opportunity on it
Zoom into the stages on the opportunity Funnel
Note that at the bottom of the stage, the boxes each indicate a number, representing the probability, and and text, representing the forecast category, in a light purple box
Click on a specific stage
Select “Settings” on the right hand side of the screen
Update the probability and forecast category fields
You may receive a warning message that states the stage is used in other Funnels, and making this change will apply to this stage in all Funnels