Switch package during contract?

[#1]

Hello,
When I purchased Plusnet Broadband the estimated speed was 60 MB. As we know Plusnet only offers either up to 16 or 72. I decided to pick 72 since it is closer to my estimate.
However my broadband has never even been over 30. Speedtests always score around 20 and not much more.
Sadly I'm still paying £34.49 (19.99+14.50)  and I don't feel that this is worth the money at all. I am paying for the up to 72 MB service and only receive 33% of the speed. I don't believe this to be fair.
My contract ends in May so it has not finished. Would Plusnet change my package to the up to 16 MB one, without renewing the contract? That way I would only be paying £24.49 (9.99+14.50) which fits my speed a lot more.
Thanks everyone.

[#2]

So you want to move from fibre to non fibre
Before doing that can you provide the following information
Result of the BT speedtest further diagnostics http://speedtest.btwholesale.com/
Current line speed from https://portal.plus.net/my.html?action=data_transfer_speed
Are the result you quote from a wired or wireless connection to the router
I believe that moving from a fibre to a non fibre product will incur a cancellation charge as the fibre product has a minimum contract length but I have no idea as to the actual numbers
Regarding your speeds if you move to a non fibre product I suggest putting your details in here to check http://www.kitz.co.uk/adsl/adslchecker.php - note that because you are on fibre you may have to limit yourself to putting in the post code - you can only try it and see

[#3]

Could you post the results from the BT diagnostic speedtest (as Jim requetsed) so we can see the IP Profile and from this speed test please: http://www.thinkbroadband.com/speedtest.html