We would normally expect DLA forms to arrive about 4 months ahead of time, so I do agree that yours are a bit earlier than usual. At least you will have a bit more time to get the form completed and evidence gathered!
We cannot tell you when to send the forms back as there are pros and cons for any action, but this might help
When should I send my renewal form back? My own reassessment forms arrived, as expected, about 4 months ahead of time and the decision was made within a few months. I was pleased to see that the decision takes effect from the expected renewal date.