Changing software from Forge to Spigot

I am trying to change my software from Forge to Spigot, but keep the world I had on the server and not lose it. I changed the software to Spigot but after copying the back-up, it reverts back to Forge. I tried downloading the world, and re-uploading it, but apparently the file size is too big.

This has been bugging me for a couple of hours, so any help is appreciated!

Thanks

So the only way for me to change software type without losing my world is to re-upload my world?