To Be Renewed
To Be Formal, To Be Altered, To Be Revised
intransitive verb, godan verb
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb.
The kanji itself means renew so the verb vocab version is to be renewed. Like most verbs ending in まる, this is an intransitive verb, meaning it happens all on its own. Nobody is doing the renewing, it's just happening (as renewing often does).
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You probably learned this reading with this verb's transitive other half 改める, but here's a mnemonic anyway just in case:
To be renewed you decide to go to a spa. You get in a bathtub and they pour in a lotta (あらた) leeches and eels to help you to be renewed. Feel the fear. There are a lot of them! Alternatively, you can imagine them pouring in a lotta Maru cats, because that's way fuzzier.
日本の年号が、豆河豚に改まりました。
The Japanese era name was altered to Tofugu.
ビエトの生活たい度が改まって、コウイチはとてもよろこびました。
Koichi was very happy to see that Viet had reformed himself from his evil way of life.
そう改まるなよ。コウイチ大統領は、とても気さくなんだから。
Don’t be so formal! President Koichi is very friendly.