How can i update version nis?

I had a trial version of nis 2009 that came as bundle with laptop, I renewed the subscription when it expired but now i am stuck with the 15.5.0 version whenever I  run the autodetect-update tool it redirects me to a page with the following msg:

 

You are not eligible for an update...

We're sorry, but your installed Norton product is not eligible for an update. Only customers with a paid current subscription are eligible to download and install updates to a newer version. Examples of ineligible products include:

- Free trials
- Expired subscription
- Products with a perpetual license instead of a subscription (for example Norton Ghost or Norton SystemWorks Basic Edition)

To renew your subscription or purchase a new Norton product, please go to symantec store
 
What can I do? Is it ok if I keep this version or do I really need to update?