Hi,

If you are using the odoo enterprise the Menu is there in the UI to access the tags. Activate developer mode and navigate to Accounting -> Configuration -> Accounting -> Account Tags, from here you can delete the tags.

IF you are using the odoo community edition, by default there is no menu to access and see the tags, here either you can add a new menu from the user interface(Action exists already in community) or you can use this free module from the OCA.

See Accounts tags Menu module: Account Tag Menu

If you don't want to use third party modules, just create a new menu from UI in debug mode and set the action as Account Tags.

See below image.

Once you have the menu, you can delete the tags by clicking the delete button in the form.

Thanks