Take your world elsewhere.

1. 1

   Take a backup.

   In the Backups tab, press Back up now and wait for it to finish. Stop the server first if you can, so nothing's half written.

2. 2

   Download it.

   Press Download on its row. You get one .tar.gz file with everything on the server in it.

3. 3

   Find the world.

   Unpack the file. The folder called world is your world. On older Paper and Purpur versions, the Nether and the End are beside it in world_nether and world_the_end.

4. 4

   Use it.

   For single-player, put the folder in the game's saves folder. If the Nether and the End were beside it, first move the DIM-1 folder from world_nether and the DIM1 folder from world_the_end into world, or they stay behind. For another host, upload it wherever they ask.

Already deleted the server? Its final copy waits on your dashboard for seven days, then it's gone for good.