How to delete a project - Visual Studio Team Services

With the latest changes done on the UI of VSTS you can navigate to https://{yourtenant}.visualstudio.com/_admin then in the Overview tab you will see a list of all the projects, select the one you want to delete from there.

If you are trying to delete a team project you can do so from the admin section reachable by clicking the gear icon in the upper-right corner of the you.

You will access the Admin section where you'll see the list of team projects. By clicking on the ... icon near the project you want to delete you''l open a dropdown with a Delete option.

For further info and a step to step guide you can refer to the official documentation