In SharePoint 2013, there is no real user interface to modify the search topology. Well, there is, but you can only use for a single server farm. If you have more servers in your SharePoint farm, you have to do this through PowerShell.
One of my South-African Premier Field Engineer colleagues Scott Stewart developed a tool on top of PowerShell WITH UI to create or modify a search topology.
Read more about it here: “Add or Modify SharePoint 2013 Search Topology using a PowerShell built User Interface”
A few screenshots to get you curious 🙂
It looks like a very promising tool! Have fun with it!