i want to delete the whole COA .

You should customize l10n_country module, or better yet, write new module based on existing localization package for your country, using your modified data ( chart template, taxes, fiscal positions etc... whatever you think should be in localization package)
Keep in mind that your custom module should be  "category": 'Localization/Account Charts', (in __openerp__.py ) 

Then create new database, install accounting and finance module ,and apply your custom chart of accounts

That should do the trick... after a few tries you will have your customized account chart template, that can be applied on any newly created database...

Hope it helps.

p.s. you cannot remove other charts once they are installed...  but you do not need to use themm...