Different Salesforce plans have different allocations of push topics. If you are at your push topic limit, you'll need to free up some available push topics by upgrading your plan or deleting push topics.
First, go to Workbench and log in with your Salesforce credentials. Navigate to "Queries" and select "Streaming Push Topics."
In the dropdown next to "Push Topic," select the push topic you wish to delete. In Distro, push topics are named in the following naming convention:
ChiliPiper-( OBJECT TYPE)
Once you've selected a push topic, click on "Details." Now, click on "Delete."
The push topic has been deleted.