The server has not yet been updated, but we're working on it and will be updated to 1.8 as soon as possible.
As for the ETA of the server update, we hope that we'll be updated in the next month. However we're still not sure, and it could be more or less than that.
If you wish to play the server, but don't know how to go back to the last version, follow this quick tutorial.
1. Open your Minecraft launcher, then click 'Edit profile'
2. Then where it says 'Use version' click the dropdown menu, and choose 'release 1.7.4', as that is the version we're currently using.