ReCT is a portable zip, so you don't actually have to install anything!
Just go to https://bytespace.tk/rect/ and download the latest version. (If you want an older one, you can find all versions here)
Now that you have the Zip, you can just unzip it anywhere you want, and that's it! You now got ReCT installed!
ReCT includes the Bolt Package Manager, which can automatically update your Installation. When there is a new Version, you will get a Popup when opening ReCT IDE asking you if you want to perform an Update. The update process after this point is completely automatic.