The core is a single direction: down. The pa'al לָרֶדֶת is to descend, to go down; the hif'il לְהוֹרִיד is its causative, to bring something down, to lower, and in the computer age, to download. From the same root come the noun descent / decline (יְרִידָה) and the adjective low-grade, inferior (יָרוּד), what has come down in quality. Two of these carry a heavy second meaning in Israeli life: a yerida is also emigration from Israel, the mirror of aliyah (going up). This is a first-yod (pe-yod) root, so the י often drops or shifts to a vowel in conjugation. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
The pa'al / hif'il pair is the classic causative contrast: laredet is to go down yourself, lehorid is to bring something else down. In the pa'al the initial י vanishes (לָרֶדֶת); in the hif'il it surfaces as the וֹ vowel (לְהוֹרִיד), the regular behaviour of a first-yod root. "Download" is simply the newest use of "bring it down".
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.