Updating XML file

Good morning, long time post sponger, first time poster here.

I'm not bad with Powershell but quite bad with XML and I'm failing to do something that seems very simple.

I have written/adapted a script to download data from an FTP site uploaded since a given datetime, which sounds hard, but wasn't too bad. Then I need towrite back the current datetime to the XML file, which sounds easy but I can't seem to do.

2 examples from the XML file:

<DataFetch version="1.0">

<DSource>

<Source>/incoming/Source1/</Source>

<Destination>C:\Temp\Source1</Destination>

<Mask>*.zip</Mask>

<ModDate>15 July 2015 00:00:00</ModDate>

</DSource>

<DSource>

<Source>/incoming/Source2/</Source>

<Destination>C:\Temp\Source2</Destination>

<Mask>*.xls?</Mask>

<ModDate>10 July 2015 00:00:00</ModDate>

</DSource>

</DataFetch>

The relevant part of the Powershell:

[xml]$XMLvar = Get-content .\DataFetch.xml

foreach( $DSource in $XMLvar.DataFetch.DSource) 

{

$CurrDate = (get-date) -as [string]

$Source = $DSource.Source

$Dest = $DSource.Destination

$Mask = $DSource.Mask

$ModDate = $DSource.ModDate

$ModDate.setattribute = $CurrDate

# $node = $DSource.ModDate 

# $node = $CurrDate

# #$xml.updateattribute $DSource.ModDate,$CurrDate

# $node

}

All of the commented out lines are bit of things I've tried that don't work at all, can anyone help?