Updating to the latest version will probably fix the one bug we had with the contribute button on the contribution page. It's also the base for further work.
The latest stable version as of today is 5.5.3.
Along with CiviCRM the CiviSEPA extension also needs to be updated from version 1.2.5 to 1.2.6
The update also will require to deactivate the Donation Receipt Extension (was deprecated with CiviCRM 4.7 and won't work anymore, but wasn't ever used until now).