sql express db limit

Hi I've a sql 2005 Express install on my system. I have a db build with sql 2005 (MY_OWN_DB) that reach 4Gb size.

If I upgrade SQL version to SQL 2008 R2, without uninstalling, my db is automaticcaly extended to 10Gb size limit?

Or should I have first to backup the db, create a new one with the same name in SQL 2008 R2 Management console and then restore the backup on the db that i have just create?

And if I detach and attach the db the size limit were update?

TIA