To save limit for active projects, you can archive or completely delete them.
How to delete project
You can delete only your own projects. Go to section All projects via Projects in upper blue bar.
Each project has three-dot menu on the right. Find section My projects and your projects have option Delete project.
In following window confirm via Delete.
How to restore deleted project
Deleted project can be restored within 30 days in section Last deleted. Check article about task overviews. You can restore only your own deleted projects.
Go to Reports > Task overviews > Last deleted.
How to delete archived project
You can delete already archived project. In section All projects find Archived projects. Click the project name and go to its detail.
In upper orange bar are 2 options: Restore or Delete a project. You have access to your own archived projects only. So you can restore / delete only those.
Faster way is via three dot menu in section All projects.
Archived project are useful when you are close to the plan limit and some of your projects are not active at the moment. Archived project can be restored anytime with all the data.
How to restore archived project
Restore archived project in section All Projects via three dot menu on the right > Restore.
Another way is via archived project detail. Click the project name and in orange upper bar click Restore.