I am guessing that (as other's have pointed out) you don't really want a cartesian on this update so I have added an "id" to the query so you will have to do some modification but this might get you on the right path
;with temp as (
select a.id, SUM(a.pazartesi - b.kota) as newTotal
from [asgdb01].[dbo].[info] a join [asgdb01].[dbo].[kota] b
on a.id = b.id
where a.work_type='in' and a.name='alp' )
update a
set fm = t.newTotal
from [asgdb01].[dbo].[info] a join temp t on a.id = t.id
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