SHOULD
Non-negative: should
Uncontracted negative: should not
Contracted negative: shouldn`t

SHOULD can express obligation and logical necessity
You should do as he says
Eg
They should be home by now
SHOULD has a putative use after certain expressions, eg: it is a pity that, I am surprised that
It is odd that you should say this to me
Eg
Eg
SHOULD also has a contingent use (1st person only and especially BrE) in the main clause (= would)
We  should  love to go abroad, if we had the chance
 
Another use of Should is in rather formal real conditions
If you should change your mind, please let us know
Eg
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