On the Pipeline page, drag and drop from one stage to another.
Process admins or project admins can change the stage of a project.
When the goals for the current stage have been accomplished, an admin may want to move the project to the next stage.
From the pipeline:
Drag it from one stage and drop it to another stage along the pipeline.
From the cover page:
Click the orange “Edit Cover Page” button on the cover page, then click on the stage you want from the stage list.