You can modify triggers through the Table Designer or through the language.

To modify a trigger 

In the Table tab of the Table Designer, enter the new trigger expression in the Insert trigger, Update trigger, or Delete trigger box. 
-or- 

Issue the SET SAFETY OFF command, and then use the CREATE TRIGGER command. 
When you modify a trigger by first issuing the SET SAFETY OFF command and then re-creating the trigger, the old trigger expression is automatically deleted and replaced by the re-created trigger expression.

OPEN DATABASE xxx.dbc
USE xxx
MODIFY STRUCTURE

CLOSE ALL
USE xxx.dbc
LOCATE FOR objecttype='Table' AND objectname='xxx'
MODIFY MEMO property

OPEN DATABASE xxx.dbc
DISPLAY DATABASE TO FILE xxx.txt noconsole
MODIFY FILE xxx.txt

Database Name:          XXX
Database Path:          c:\...\xxx.dbc
Database Version:        10 

Database   StoredProceduresDependencies
...
Table      xxx
           *Path            xxx.dbf
           *UpdateTrigger   IIF(MESSAGEBOX( "xxx" , 36 )= 6 ,.T.,.F.)
           Field      id
           Field      fio
           Field      postind
           Field      address
...