eBay will not let you edit or update any information about your products listings directly on the eBay.com website if your products were listed with software. They will direct you back to the software to edit those data attributes via their API.
Here is how you edit the price, quantity and other attributes on your eBay listings.
Navigate to Inventory > Live eBay Listings
Then find your product and click on the pencil edit icon
Once finished, simply click the Update on eBay button.