There is a subforum called "C# Installation" for exactly this purpose. The sticky threads always contain what you need to install the game. Refer here in the future when updating to a new game version.
The usual instructions would be to download the complete installation for 1.13 I think and then manually download each update/patch in the order they were released and replace the files they mention, but I think only the .exe and the dabatase file changed, so I **think** you can just download the 1.13 installation and then 2.5 and 2.5.1 respectively instead of going through all of them one by one?