To disable the module it is enough to edit app/etc/modules/Unirgy_Giftcetrt.xml and make sure <activ>true</active> is changed to <active>false</active>. Disabling from Admin System>Configuration>Advanced is not going to work.

If full removal is needed, then all extension's files should be removed. These are:

• app/etc/modules/Unirgy_Giftcetrt.xml
• app/code/community/Unirgy/Giftcert/
• app/design/adminhtml/default/default/layout/ugiftcert.xml
• app/design/adminhtml/default/default/template/ugiftcert/
• app/design/frontend/base/default/layout/ugiftcert.xml
• app/design/frontend/base/default/template/unirgy/giftcert/
• js/colorpicker/
• app/locale/en_US/Unirgy_Giftcert.csv
• app/locale/de_DE/Unirgy_Giftcert.csv
• app/locale/fr_FR/Unirgy_Giftcert.csv
• app/locale/it_IT/Unirgy_Giftcert.csv
• app/locale/ja_JP/Unirgy_Giftcert.csv
• app/locale/nl_NL/Unirgy_Giftcert.csv
• app/locale/en_US/template/email/ugiftcert_self.html
• app/locale/en_US/template/email/ugiftcert_recipient.html
• app/locale/de_DE/template/email/ugiftcert_self.html
• app/locale/de_DE/template/email/ugiftcert_recipient.html
• app/locale/fr_FR/template/email/ugiftcert_self.html
• app/locale/fr_FR/template/email/ugiftcert_recipient.html
• app/locale/ja_JP/template/email/ugiftcert_self.html
• app/locale/ja_JP/template/email/ugiftcert_recipient.html
• app/locale/pt_PT/template/email/ugiftcert_self.html
• app/locale/pt_PT/template/email/ugiftcert_recipient.html
• skin/adminhtml/default/default/ugiftcert.css

If you want to remove all database traces of the module you should:

DROP TABLE `ugiftcert_cert`;
DROP TABLE `ugiftcert_history`;
DELETE FROM `eav_attribute` WHERE `attribute_code` LIKE '%giftcert%';
DELETE FROM `catalog_product_entity` WHERE `type_id`='ugiftcert';

Removing databse entries is not required except of

DELETE FROM `eav_attribute` WHERE `attribute_code` LIKE '%giftcert%';

which will prevent any PHP errors due to missing classes for GC attributes. If you want you can scan sales_flat tables for any %giftcert% columns and remove them.