Follow below steps to change the order status in Magento 2
Step 1:- Login to your admin panel.
Step 2:- Go to SALES -> Orders and click on it as image below.
Step 3:- Click on a view link to view the order details
Step 4:- Now click on Invoice button.
Step 5:- Add invoice comment in the comment box and checked on Append Comments if you want to add comment in the email and checked on Email Copy of Invoice if you want to send copy of email. Finally click on Submit Invoice.
Step 6:- Now you can see that your order status is changed from pending to processing.
Step 7:- Then click on Ship button.
Step 8:- Add Shipment comments in the comment box and checked on Append Comments if you want to add comment in the email and checked on Email Copy of Shipment if you want to send copy of email. Finally click on Submit Shipment.
Step 9:- Finally you can see the order has been changed from processing to Complete. In this way, you can change the order status.
Please contact us at manish@bay20.com or call us at +91-8800519180 for any support related to Magento 2. You can also visit the Magento2 development page to check the services we offer.