modifying value using XML DOM

[051984]

How can i modify the value in the last field "491" and i need to run 500 times and on each iteration I can see this value is incrementing . I am using QTP to compile this code but I am not able to modify this value????
Can somebody help me in modifying the value("491")?????
Thanks

<abc-tag-imagemark number="45" offset="1391" len="90">
<im-batch-info number="3">
<field type="schar" size="4" name="batch_number" desc="batch number registered in DocNumAPI">1321</field> <field type="uint4" size="1" name="mfilm_frame_num" desc="microfilm frame number">0</field> <field type="uint4" size="1" name="mfilm_cartridge" desc="microfilm cartridge number">0</field> <field type="uint4" size="1" name="entry_number" desc="entry number registered in DocNumAPI">491</field>
</im-batch-info>
</abc-tag-imagemark>