• Basic forms
• 代わる — to replace / to take someone’s place / to switch / base form
• 代わります — (it) replaces / (someone) takes over / masu form
• 代わった — replaced / changed / ta form
• 代わって — replace (and…) / please replace / te form
• 代わらない — does not change / negative
• 代われば — if it changes / if (someone) takes over / conditional
• 代われ — take over! / imperative
• Other common forms
• 電話を代わる — to take the phone for someone
• 担当が代わった — the person in charge changed
• 気が代わる — mood changes (slightly figurative)
• More
• 代わろう — let’s switch / let’s take turns / volitional
• 代わらなかった — didn’t change / negative past
• 代わっている — is replacing / is functioning as / progressive

代わる（かわる） is a godan る-verb. It means “to take someone’s place,” “to change,” or “to switch roles.”