Under manage booking, two options are given: Acknowledge Changes (flight times/dates were changed) or Request a refund. I don't want to cancel as I just want to change the dates. I also don't want to acknowledge changes. I am trying to reach Qatar customer service via telephone and I have waiting on the line for the last 45 minutes for a customer service agent.
Try twitter if you have an account. I have been able to reach them via their twitter. They may take hours or even days to respond but they eventually do and everything is in writing so no need to repeat yourself.
If using twitter, provide the booking reference, both names on the reservation, email and phone number on the reservation and the date you purchased the original
ticket. Also add the suggested new itinerary if you have already looked it up. This will save you a lot of time.
I don't think there is any harm in acknowledging the changes and then attempting to change the flight. The conditions of the ticket provide for unlimited free changes. However it's up to you what you are comfortable with.