In this tutorial, you will get to install your desired Feed the Beast modpack on a server.
You will be using FTP to upload/download files. Please refer to this tutorial if you do not know how to transfer files via FTP.
How to: FTP file access - https://ggservers.com/billing/knowledgebase/13/How-to-FTP-File-Access.html
If you want to keep your world or keep any of the current server files, download whatever files you wish to keep to your personal computer via FTP.
Download the Feed the Beast Launcher: http://www.feed-the-beast.com/
Open the launcher and select the modpack you wish to play. Click Download Server.
Extract the downloaded zip file, then open your FTP client. Connect to your server, and delete the ServerStart.bat or ServerStart.sh as you do not need them.
Upload the FTB Server jar. Rename the jarfile to either "permgen.jar" or "ftb.jar" and then upload. Set your server to run on that jar. ( Use the following guide for a brief summery on how to upload and set your server jar: https://ggservers.com/billing/knowledgebase/3/How-to-Upload-and-use-your-own-JAR.html Remember to press SAVE. )
If you are running a FTB modpack minecraft version 1.5.2 or earlier, upload ALL sub folders to the root of your server (mods, coremods, and config folders).
If you are running a FTB modpack minecraft version 1.6.4 or later, upload the 'libraries' folder into the 'jar' folder (where your ftb.jar server jar is located), and other sub folders to the root of your server (mods and config folders).
After uploading all server files, start your server.
If you have any questions or need help, feel free to submit a ticket. If you have the Modpack Installation and Support add-on, we can help you install the modpack.