We support batch delete of rows in the UI. You can select up to 200 rows and delete them at once.
That however might not be feasible when number of rows is high. In that case API calls can be used to perform those operations. You can find information on generating API keys here.
If you're familiar with programming, you can use get and delete API calls. Here is an example python script that gets all rows and updates them - Python script for updating rows in a table.
For business and enterprise plans we have Automatic old row cleanup feature that can help stay within limit by automatically deleting oldest rows from selected table.