SQL update query

Hi, Can someone please help me with this SQL update query. Hopefully its fairly obviosu what I am trying to do but the syntax is wrong .... missing expression.

update subscriber_questions set answer_text = 'Employ\u00E9'
where
(select a.answer_text from subscriber_questions a, subscribers b
where b.subscriber_code = a.subscriber_code
and b.site_id = 'XXX'
and a.country_iso_code = 'UK'
and a.question_code = 'OCCUPATION'

update subscriber_questions set answer_text = 'Employ\u00E9'
where NOT EXISTS | EXISTS
(select a.answer_text from subscriber_questions a, subscribers b
where b.subscriber_code = a.subscriber_code
and b.site_id = 'XXX'
and a.country_iso_code = 'UK'
and a.question_code = 'OCCUPATION')

You suppose to compare the returning value of subquery with the column of outer query or just check the existance or non existance (only use EXISTS or NOT EXISTS at a time not both in a single search condidtion)of some value in the subquery as mentioned above.
To compare the value of subquery with the outer query column, use the following example:

update subscriber_questions set answer_text = 'Employ\u00E9'
where answer_text =
(select a.answer_text from subscriber_questions a, subscribers b
where b.subscriber_code = a.subscriber_code
and b.site_id = 'XXX'
and a.country_iso_code = 'UK'
and a.question_code = 'OCCUPATION')