After I have replaced some stages with new stages they are still listed under active. When I tried the change with a test record in the sandbox it has been updated with the new stage, so it works. However, the old stage is still in the active list. Can I delete it? What do I have to do so all the old stages are replaced with new ones and only the new ones are available as options when new opportunities are created?
To ensure the stage names are not used you will need to replace them. You can also remove them from being available to pick by editing the Sales Processes.
To move the Stage to inactive, simple click "Del" next to the stage...
Sales process stages, for example, Prospect, Proposal. This picklist also affects the Type and Forecast Category values of an opportunity. Specifically, changing the Type or Forecast Category for a Stage picklist value updates all opportunities that have that stage value.
To edit, from the management settings for opportunities, go to Fields, and then click Edit next to Stage.
To deactivate an active stage, click Del next to the stage. On the mapping page, don't replace the stage with another existing value; just click Save. The stage now appears in the Inactive Stage Picklist Values related list. The stage is no longer in use but may exist in older opportunity records.