How do I exchange old 1 coins?

Hello there, I'm curious about a process that's been on my mind lately. Could you please elaborate on the steps involved in exchanging old 1 coins? I've heard that some currencies have undergone changes over time and I'm wondering how one goes about converting these older coins into their current, valid form. Are there specific places or procedures I should follow? Additionally, are there any potential pitfalls or fees I should be aware of during this process? Your insight would be greatly appreciated.