You will need to make sure that the Windows account which the SQL Server service is running under has full control to the folder which has the backup file as well as the file, as well as the folder which you want to restore the database to.
You may also need to go to the second tab of the restore window and change the paths to the database files. You can also use the RESTORE DATABASE command manually to restore the database using the WITH MOVE option to specify where you want to restore the database to.
If you are still getting the error message please post the entire error message. Without the full error message I’m just guessing here.