[ADDITIVE] && See HELP for SET RELATION command. it just in case You have additional relations between theese two tables, If You don't do not put ADDIDVE in command i.e.
YUou have old relations between tables

SET RELATION TO Key INTO Table2 ADDITIVE

If You Don't

SET RELATION TO Key INTO Table2 && noting else

about the Key, no That is no Primary Key, That is field on what theese two tables correspond each other and YES You must have an index (not necessary to be PRIMARY)
i.e. You have field in table A named Code, Id, or something else, let say it is ID, In Table2 (nan) You must have a field that contains exatly the same data (not necessary that all Ids in Table2 are in Table A)
i.e.

CREATE CURSOR Table1 (Id  C(10), Field1 C(20), Field2 C(20))
CREATE CURSOR Table2 (Id1 C(10), Field1 C(20), Field2 C(20), Field3 N(15,2))
tosmall = 0
FOR nCikle = 1 TO 300
    IF nCikle < 151
       INSERT INTO Table1 VALUES (TRANSFORM(nCikle), "Record"+TRANSFORM(nCikle), "Other"+TRANSFORM(nCikle+5))
    ENDIF
    IF nCikle < 160
       to_replace = nCikle
    ELSE
       to_replace = nCikle  - tosmall
       tosmall    = tosmall + 1
    ENDIF
    INSERT INTO Table2 VALUES (TRANSFORM(to_replace), SYS(2015), SYS(2015), nCikle)
ENDFOR
SELECT Table1
INDEX ON Id TAG Table1
SELECT Table2
GO TOP
BROWSE NORMAL
SET RELATION TO Id1 INTO Table1
REPLACE ALL Field1 WITH Table1.Field1,;
            Field2 WITH Table1.Field2,;
            Field3 WITH Table1.Field3;
FOR .NOT. EMPTY(Table1.Id) && Just in case You have no matching records
SET RELATION OFF
GO TOP
BROWSE NORMAL