FoxPro doesn't support JOIN in UPDATE/DELETE SQL commands. You can use combination of SCAN...ENDSCAN and UPDATE. Something like

SELECT test2
SCAN FOR test2.field2 = '123456' ;
    and test2.field4 = '789102' ;
    and NOT test2.field5 and NOT test2.field6
  Update test1 Set test1.field1 = 10 ;
  WHERE test1.field3 = 'TEST' ;
    and test1.field2 = test2.field2
ENDSCAN

>I am trying to do an update with joins. I cannot get this to work in FoxPro. Do I have something wrong with my update, or is this a limitation in FoxPro?
>Here is the code:

>Update test1 ;
>Set test1.field1 = 10 ;
>  from test1   ;
>  inner join test2  ;
>    on test2.field2 = test1.field2  ;
>  WHERE test2.field2 = '123456' ;
>    and test1.field3 = 'TEST' ;
>    and test2.field4 = '789102' ;
>    and test2.field5 = .f. and test2.field6 = .f.