How to delete all orders from Magento?

Go to Phpmyadmin and run following sql code:

SET FOREIGN_KEY_CHECKS=0;

TRUNCATE `sales_flat_creditmemo`;

TRUNCATE `sales_flat_creditmemo_comment`;

TRUNCATE `sales_flat_creditmemo_grid`;

TRUNCATE `sales_flat_creditmemo_item`;

TRUNCATE `sales_flat_invoice`;

TRUNCATE `sales_flat_invoice_comment`;

TRUNCATE `sales_flat_invoice_grid`;

TRUNCATE `sales_flat_invoice_item`;

TRUNCATE `sales_flat_order`;

TRUNCATE `sales_flat_order_address`;

TRUNCATE `sales_flat_order_grid`;

TRUNCATE `sales_flat_order_item`;

TRUNCATE `sales_flat_order_payment`;

TRUNCATE `sales_flat_order_status_history`;

TRUNCATE `sales_flat_quote`;

TRUNCATE `sales_flat_quote_address`;

TRUNCATE `sales_flat_quote_address_item`;

TRUNCATE `sales_flat_quote_item`;

TRUNCATE `sales_flat_quote_item_option`;

TRUNCATE `sales_flat_quote_payment`;

TRUNCATE `sales_flat_quote_shipping_rate`;

TRUNCATE `sales_flat_shipment`;

TRUNCATE `sales_flat_shipment_comment`;

TRUNCATE `sales_flat_shipment_grid`;

TRUNCATE `sales_flat_shipment_item`;

TRUNCATE `sales_flat_shipment_track`;

TRUNCATE `sales_invoiced_aggregated`;

TRUNCATE `sales_invoiced_aggregated_order`;

TRUNCATE `sales_order_aggregated_created`;

TRUNCATE `sendfriend_log`;

TRUNCATE `tag`;

TRUNCATE `tag_relation`;

TRUNCATE `tag_summary`;

TRUNCATE `wishlist`;

TRUNCATE `log_quote`;

TRUNCATE `report_event`;

ALTER TABLE `sales_flat_creditmemo` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_creditmemo_comment` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_creditmemo_grid` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_creditmemo_item` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_invoice` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_invoice_comment` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_invoice_grid` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_invoice_item` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_order` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_order_address` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_order_grid` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_order_item` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_order_payment` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_order_status_history` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote_address` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote_address_item` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote_item` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote_item_option` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote_payment` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_quote_shipping_rate` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_shipment` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_shipment_comment` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_shipment_grid` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_shipment_item` AUTO_INCREMENT=1;

ALTER TABLE `sales_flat_shipment_track` AUTO_INCREMENT=1;

ALTER TABLE `sales_invoiced_aggregated` AUTO_INCREMENT=1;

ALTER TABLE `sales_invoiced_aggregated_order` AUTO_INCREMENT=1;

ALTER TABLE `sales_order_aggregated_created` AUTO_INCREMENT=1;

ALTER TABLE `sendfriend_log` AUTO_INCREMENT=1;

ALTER TABLE `tag` AUTO_INCREMENT=1;

ALTER TABLE `tag_relation` AUTO_INCREMENT=1;

ALTER TABLE `tag_summary` AUTO_INCREMENT=1;

ALTER TABLE `wishlist` AUTO_INCREMENT=1;

ALTER TABLE `log_quote` AUTO_INCREMENT=1;

ALTER TABLE `report_event` AUTO_INCREMENT=1;

SET FOREIGN_KEY_CHECKS=1;