I am new to the programme and accidentally imported the worksheet in the wrong language.
Is it possible to remove the worksheet and/or to replace it with the desired Language?
You don't have to delete it. Just import the correct workbook.
(Deleting the info is possible though: in Settings | LMM Meeting | Schedule tab: select the weeks in the top box one by one, and click the minus sign next to it.)
For accessing the database my personal preference is http://sqlitebrowser.org/
For editing templates I like to use http://brackets.io/