Thanks John,
That worked!
This powershell script does the trick:
$gm=New-Object -com FSRM.FSRMGlobalStoreManager
$s=[xml]$gm.GetStoreData("Settings", "ReportSettings")
$s.Save("c:\temp\fsrm-reports-backup.xml")
$s.root.MaxQuotas="10000"
$gm.SetStoreData("Settings", "ReportSettings",$s.get_InnerXml())