This short article will show you how to Mass delete Category and Tags in WordPress without a plugin.
1—Log into your Dashboard (Admin panel) of WordPress
2—Go to Post Tags (or Post Categories as the case may be) under the Posts section in the sidebar
3—Click on the Screen Options link given on top right corner of your screen
4—Enter a numeric value in “Show on screen” box (the maximum it will take is 999) and Click Apply button
5—The page will now reload to show 999 tags on one page.
6—Select all of them by checking the checkbox to the left side of Name header
7—Select “Delete” from Bulk Action dropdown and click Apply
How to Mass delete Category and Tags in WordPress without a plugin