Detached large database and cannot attach it again

Hello,
i am using SQL Server 2012 Express. I have a service, which writes to a database, and the database reached the limit 10 GB. The service tried tried to write data to DB very often, but couldnt because of the limit, and every unsuccessfull try generated an error log, which started to eat up my harddisk space.
To the point: For some reasons the best option for me was to detach the database, untill i could adress the problem. But when I tried to reattach the database, i could not, because the create for attach query ended with error "CREATE DATABASE or ALTER DATABASE failed because the resulting cumulative database size would exceed your licensed limit of 10240 MB per database."
How can I attach the database, or reduce its size before attaching it?
Thanks.