You can change your Packlink PRO password from your customer account.
You have to log into pro.packlink.es and access "Settings > Your Account", where you’ll see "Change password"
Log into your Packlink account > Settings > Your Account > Change password
If you want to change it because you don't remember it, in the upper right area where you access your account, you can click on the option: "Forgot password?". Then you will receive an email with a new one. :)