Detach the database, then move the transaction log to the new location and re-attach the database.
Examples:
EXEC sp_detach_db 'pubs', 'true'
EXEC sp_attach_db @dbname = N'pubs',
@filename1 = N'c:\Program Files\Microsoft SQL Server\MSSQL\Data\pubs.mdf',
@filename2 = N'c:\Program Files\Microsoft SQL Server\MSSQL\Data\pubs_log.ldf'
You can serach books online for more help sp_detach_db and sp_attach_db..