1. download last version
2. in Blender go to File » User Preferences » Add-ons Tab
3. remove previous installation if needed (search retico to easily find it)
4. click on Install... button on select retico_vXXXX.XX.XX.zip file

ReTiCo is now available in 3DView » Sidebar » ReTiCo tab.

As I develop mainly using last stable Blender version, on activation you may seen this kind of warning: This script was written Blender version 2.81.0 and might not function (correctly), though it is enabled. Don't worry, it should be OK.

Tip: once installed, configure the UI of ReTico as you want and use File > Defaults > Save Startup File to keep it as it each time you're launching Blender.