How to discover switch IP's and credentials? (Networking noob)

Hello,

I'm a SysAdmin and a networking noob....I have been tasked with the following:

Upgrade (firmware) and refresh credentials on all switches across the environment.

We have multiple locations across the US and there are probably 15 switches. The problem is the previous regime didn't document any switch IPs or creds.

My question is, how can I discover the switches and somehow obtain the admin creds? To the best of my knowledge they are all Cisco switches. If needed we can reset them but that is a last resort.

Thanks and sorry for the silly question.