How to delete Large Object from Database?

Dear All,

 

I use '$libdir/lo' for manage my PostgreSQL Large Object. It work fine for me to get and put Large Object  from and to database. However I found something that may not correct when I try to backup my data. It seem that I cannot delete Large Object from database. It seem the thing I can do is only delete the reference oid from table but Object still in database.

 

A Detail shown below is  reason I think that I cannot delete Large Object out of database.

 

14MB of file size when BackUp Data (BLOB Included)