Recently I needed to do this for our PRTG alerting account which was failing to send notifications as the O365 password had expired. I did this from Powershell within Windows 10 as follows:
Launch powershell as Administrator then run
[cc lang="powershell"]Install-Module MsOnline[/cc]
Then run
[cc lang="powershell"]Connect-MsOlService[/cc]
at this point an O365 authentication box pops up – enter your credentials. Once connected run:
[cc lang="powershell"]Set-MsolUser -UserPrincipalName user@contoso.com -PasswordNeverExpires $true[/cc]
Some of these commands have since been deprecated. For an explanation look at this post.