The quick release lever right under the fender mount is what secures the seat; no tools required.
You will have to loosen the fender if you want to move the seat down.
BTW, if you are that unfamiliar with bicycles I suggest you take it to a bike shop (preferably one that sells Raleighs) and ask them to give you a run-through on how it works...
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Today, I believe my jurisdiction ends here...