As part of the ongoing effort to move out of the old app, we've been moving more administrator functionality into the web app. We actually have a new Admin menu now:

And one of the recent things we've added to it is the same student merge functionality that has always been part of the old desktop app. Here's what it looks like in the web app:

You can play with it a bit here. The Admin menu will be the home of lots of new functionality like this.