If you do not need any of the existing projects within your Azure DevOps organization, follow the below steps to delete the project.
Login to your azure DevOps organization at https://dev.azure.com/{yourorganizationname}.
Open the Azure DevOps project you want to delete > Project Settings > Overview > Scroll down till the end > Delete > Enter the Project name > Delete.
Fig 1 - Delete from Azure DevOps Project settings
Other way to delete > Select organization > organization settings > Projects > Select Project > Delete > Enter the Project name > Delete.
Fig 2 - Delete from Azure DevOps organization settings
Note: To delete the project, you must be the project administrator role with Delete team project permission.