Edit specific Element in XDocument

Edit specific Element in XDocument

thanks for taking the time to answer my question. I recently started
learning C# and I ran into a problem using XML.Linq to store data. I hope
the question is understandable as I am not familiar with all the correct
terms yet and as English isn't my first language.
I read a lot of Questions/googled but I can not figure it out myself.
I want to update an existing XDocument File that looks like this:
<Data>
<IDCounter>2</IDCounter>
<Highscores>
.......
</Highscores>
<savegames>
<savegame>
<IdNumber>2</IdNumber>
<salutation>Mr</salutation>
<prename>Prename1</prename>
<surname>Surname1</surname>
<maximumbalance>100</maximumbalance>
<balance>100</balance>
</savegame>
<savegame>
<IdNumber>2</IdNumber>
<salutation>Mr</salutation>
<prename>Prename2</prename>
<surname>Surname2</surname>
<maximumbalance>100</maximumbalance>
<balance>100</balance>
</savegame>
</savegames>
</Data>
What is the easiest way to change a value in a specific Element?
Let's say I want to change the "balance" of a specific "savegame".
I want to access the savegame by "IdNumber" (these numbers are unique)
Then I want to change the value of "balance" (for example to 50) and then
save these changes to my document.
Thank you in advance!