Initial contract ending soon - change product + renew line rental saver ?

[#1]

From tomorrow i'm into my last month of my Plusnet Value 10GB/month service.
I would like to change to the current equivalent product (Plusnet Essentials) once the contract finishes; as it is a bit cheaper (5.99 v 6.49).
I would also like to renew Line Rental Saver for the coming year (preferably before 1st October  ;)).
Looks like I can do the first thing online easily enough ("product change" in control panel).
Is there a way to renew line rental saver online and how soon before end of contract can I do it?
According to terms/conditions I will be switched to a rolling monthly contract after the initial term, but...
If I change product, will I start another 12 month contract or continue on the rolling contract?

[#2]

To be going on with have a look here regarding line rental https://portal.plus.net/apps/linerental/saver/portal

[#3]

cheers, that page is certainly very well hidden, can't find a link anywhere in the member's centre 

[#4]

That is a good link. Turns out I have a month more left on my prepaid line rental than I thought!