*A note, Tekkit client version must be installed on your computer and all your players if they wish to join*
**You must have server jar access for this. If you do not have server jar access, You can change it under "advanced settings" in your multicraft control panel. You can't install this or other mods without this**
1. Stop your server
2. Download the tekkit server files (zip) from here: Tekkit
3. Unzip the files (using 7zip) If you don't yet have this program you can download it from the link near the top of this page.
4. Log into Filezilla using the information you get from click files, ftp access. As the image below shows.
5. Using Filezilla upload all the unzipped files into the main directory. If you don't have Filezilla download the client version from the link near the top of the page.
6. Rename Tekkit.jar to custom.jar in your files, then choose Mod: "Custom jarfiles use this" from the server drop down JAR file selection menu (If you do not see it in the drop down, Type custom.jar into the JAR file box that is shown highlighted in the image below.)
7. Click save you need to make sure you do this step or it will try to load your last jar file you had selected.
8. Start your server