urgent: update but comparing the values of two table

Hello.

I have table 1 and table 2. In table 2 I want to updata field1 to 'S' for
all records that match with table 1.

I'm trying to use this:

UPDATE EI_GESMIMS inner join EI_GESMIbk
(EI_GESMIMS.GFMSMI = EI_GESMIbk.GFMSMI) AND
(EI_GESMIMS.EMBSMI = EI_GESMIbk.EMBSMI) AND
(EI_GESMIMS.MODSMI = EI_GESMIbk.MODSMI) AND
(EI_GESMIMS.NIISMI = EI_GESMIbk.NIISMI) AND
(EI_GESMIMS.SOCSMI = EI_GESMIbk.SOCSMI) SET
EI_GESMIbk.AINSMI = 'S'

Please help me out here.

Thanks,
Marco