When a vocab word is a single kanji and doesn't have okurigana (hiragana attached to the kanji) it usually will use the kun'yomi. Since you learned the on'yomi reading of the kanji, we'll need to use a mnemonic to learn the reading of this vocabulary word.
Above you is a huge weight. You're holding it up and struggling (it's heavy!). You look up and try to crane your neck to see how much it weighs (うえ), but you can't see the numbers on the side of it. How long can you hold it above your head like this?
Please look at the chart above.
The Tofugu office is three floors up.
One of your socks was at the top of the stairs.