After SharePoint migration from 2010 to 2013, I have imported a solution, using power shell, which was developed for the SharePoint 2010. Now the feature is deployed and is available but does not working properly due to the change of SharePoint server and the URLs (I think!). How can open this feature and manipulate it using visual studio 2015?
You would need the source code of the application. If you don't have this, it is going to be a little tougher, but you can use an application like .NET Reflector to decompile the application (which won't be the same as the source), grab the on-disk files of the application (which you can also find in the WSP if you extract it), and then build a new solution based off of that.