File rename is a topic that seems to keep recurring.
The simple answer is that you use Rename-Item
PS> Rename-Item -Path C:\test\Newoutdata01.txt -NewName OldData01.txt
If for whatever bizarre reason you have a character such as [ in your file name the rename won’t work
PS> Rename-Item -Path C:\test\New[outdata02.txt -NewName OldData02.txt
Rename-Item : Cannot retrieve the dynamic parameters for the cmdlet. The specified wildcard character pattern is not valid: New[outdata02.txt
At line:1 char:1
+ Rename-Item -Path C:\test\New[outdata02.txt -NewName OldData02.txt
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidArgument: (:) [Rename-Item], ParameterBindingException
+ FullyQualifiedErrorId : GetDynamicParametersException,Microsoft.PowerShell.Commands.RenameItemCommand
The way round that is to use –LiteralPath
PS> Rename-Item -LiteralPath C:\test\New[outdata02.txt -NewName OldData02.txt
If you need to rename a bunch of files use Get-ChildItem and pipe the results into Rename-Item