Editing Project for the buyer

Hello, I recently uploaded an application and it was approved, people started commenting and requesting changes, now the question is how can I make changes in the project according to their requests. Where should I upload it?

If you mean the changes as update or new feature, you can update the item on your profile page.
If what you’re performing is custom changes/modifications for only one client, you don’t need to update the item.

What I want is performing custom changes/modifications for clients, how will I provide them the edited version?

First of all, you may be entitled to charge additional payment regarding to the project. Secondly, you can just send the file via email. You don’t need to update the main file but make sure the item is downloaded so they won’t request a refund after getting the file.