How to Upgrade solution to get the newly added feature

Hello,

I have a scenario like following:-

1. Have a solution deployed already

2. Solution have a feature which creates a list on activating and deletes the list on deactivation.

3. Now modified the exsisting solution as the list should not be deleted.

4. Feature will create the list if the list not exists only.

5. Added some others features.

Now I need to update the new .wsp but it does not reflect the latest added features untill I retract the old one and deploy the new one. If I retract the old one, it deletes the existing list(point#2) which I dont want as the list has lots of data.

So what should be the proceedure by which I can update the latest wsp and get the newly added feature without deleting the exsisting list?

Thanks in advance.