Using PowerShell to Convert From JSON to CSV format

ConvertFrom-JsonToCsv.ps1

function ConvertFrom-JsonToCsv {
    param(
        [Parameter(ValueFromPipeline)]
        $json        
    )

    Process {
        ($json | ConvertFrom-Json) | ConvertTo-Csv -NoTypeInformation
    }
}

'[{"Column 1": "1-1","Column 2": "1-2","Column 3": "1-3","Column 4": "1-4"},{"Column 1": "2-1","Column 2": "2-2","Column 3": "2-3","Column 4": "2-4"},{"Column 1": "3-1","Column 2": "3-2","Column 3": "3-3","Column 4": "3-4"},{"Column 1": 4,"Column 2": 5,"Column 3": 6,"Column 4": 7}]' | 
    ConvertFrom-JsonToCsv 

Could you help me how to run this script in Powershell ISE?
I've come to the following steps but keep getting errors

1. Stored the above script in location C:\Users\Bob\PowerShellTest\ConvertFrom-JsonToCsv.ps1
2. Stored a file in the same location named MyTest.json
3. Open powershell
4. Type + enter: cd C:\Users\Bob\PowerShellTest
5. Type + enter: .\ConvertFrom-JsonToCsv.ps1 .\MyTest.json

How should I call the file as an argument?

This is not a script but a Powershell function. In a script you would source that file and the ncall the function as in the example on line 12