Change password of multiple Cisco routers and swtiches

With that number of devices I would recommend setting up some sort of central authentication and authorization infrastructure ... like Radius or Tacacs+ ... both services can be run with free software on either Unix/Linux or Windows based servers. Tacacs will even let you define specifically which commands and functions each user can use, allowing for lower and higher level admin rights. Then, just add some very cryptic passwords (could be device specific) that are stored safely in case there are problems with reaching the authentication server(s).
Also, as a side note, make sure you have access lists configured on the devices in order to limit device access to your management network (if possible) ... and also, try to stick to SSH instead of telnet for management, just to be a bit safer ;)

Do the devices have telnet and/or ssh configured and do they all have unique passwords currently?  Do they need to have unique passwords when you are done?

Cisco snmp tool can do the job

There are quite a few variables here.  Do you have a budget?  Can you spin up a VM/appliance to run a management tool?  Do you want just a batch/bash script?

Thanks Predrag!! kiwi cattols did save my life and was easy to manage that allow me to complete the changing in a morning. I would also further look into Garry`s suggestion on building a TACAS+ while budget is not an option.