Thanks for joining in this thread, @Hamid Sharifi. I'd be delighted to answer your first post. 

Deleting inventory items completely in QuickBooks Online is currently unavailable. I understand this is relevant to you and your business. This will be a great idea we can put forward to our developers. 

Please know that all our suggested plans are subject for further study. Any developments and enhancements will be posted on our QuickBooks Blog. I'd recommend you visit our site regularly to be updated. 

For future reference, you can read through our help articles in case you'll need some easy steps on changing item types and adjusting inventory items in QBO. 

I'm always around here to provide additional support if you have further questions about inventory items, @Hamid Sharifi. Take care.