sql2008 - How to limit memory usage in Reporting Services

I read from teh mcsft website saying  as setting below in rsreportserver.config file will set the limit of memory usage in SSRS.

<MemorySafetyMargin>80</MemorySafetyMargin>
      <MemoryThreshold>90</MemoryThreshold>
      <WorkingSetMaximum>4000000</WorkingSetMaximum>
      <WorkingSetMinimum>2400000</WorkingSetMinimum>

But inside the rsreportserver.config where should I place this code setting ? I'm attach as well rsreportserver.config for  review.
rsreportserver.txt