1. Go to https://serverjars.com/
2. Download the Jar you want
3. Press File Management on the Pterodactyl panel (https://control.sparkedhost.us)
-> Picture: http://prntscr.com/kaj2k6
4. Press Upload and select the Jar you downloaded
-> Picture: http://prntscr.com/kaj3wh
5. Rename your Jar in File management (or before you upload it) by going to the 3 dots, clicking it and pressing rename. Rename it to server.jar unless you changed your Jar name in the startup parameters section.
6. Go to console and press start
7. If you get an error, delete your worlds. That is the most likely fix.