Hi @Katrina_LM, welcome to the Asana Community Forum!
I recommend you creating a project called “Archived tasks”, multi-home those tasks in this project and then remove them from your main project. This will help you clear your project and still keep the tasks for reporting purposes.
If you ever need to delete these tasks, @LEGGO posted a great tip to delete projects: Best Practices when deleting a Project
I hope this helps! 