If QTP 10 scripts are stored in QC , then you can use Asset upgrade tool to upgrade all QTP tests to QTP 11.
If you do not use QC , the you have to open indivially and resave. Basically , as soon as you open a older version QTP script with QTP 11 , it will give a popup box saying you need to convert the script to QTP 11.
Once converted , it can't be made undone. Later you can save.
So it depends on whether you have QC now or not for using the tool.
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