how to release a transaction lock on a table?

Hello everyone.  I am trying to do an ALTER TABLE, but it hangs
indefinitely.  I think the table is locked from a transaction, and in
pg_locks I found:
relation  75907
database 74861
pid 29604
mode AccessExclusiveLock
granted f

Is there a way to release this lock?  Or does the database need to
re-started?

Si