How do i stop aphids from coming in through the windowsill?

they are really gorss???? they crowd all over the windowsill and they are black and gross and their corpses litter our house but i cant wipe them because they spread like blodd ????? please help!!!!!!!!!!!!!!!!!!!!!!!
Update: edit do NOT say aphid spray i have used it . did not wrok. they keep coming. do i need to reseal my windows? if so, how????
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