How to set custom upload form for existing specific document library in sharepoint using visual studio?
A custom aspx page would be possible though，but editing the OOTB upload.aspx in the 14 hive would make your environment unsupported, the next time you install an update for sharepoint, your changes could be overwritten. Modifying any OOTB page will impact all applications running on the same farm. What ever your custom requirement always copy the OOTB page to a subfolder and try work on that copy.
I'm pretty sure doing this with infopath is not possible, the forms should be bound to a (codebehind) class in the SharePoint object model, which handles the actual upload (add to list, set field values etc. etc.).
Meanwhile, here is one article on custom upload form for your reference.
EDITED: Have a look at the below links to