A Project will often require multiple experiments. You can create a new experiment inside of a Project by clicking on the red "+Experiment" button on the top right of the Project page.
You can delete the experiment only from inside the Experiment page. Navigate inside the experiment, click the three dots on the top right, and select "Delete Experiment." You will be prompted to type in the name of the Experiment (to make sure that you aren't accidentally deleting the project).