update Iceweasel
 

how do I update iceweasel or better still remove it and replace it with firefox?

Depends on the version of Debian installed. "apt-get install firefox" could work.
edit: https://wiki.debian.org/Firefox

firefox-esr was installed for me on Jessie Stable.

"Depends on the version of Debian installed. "apt-get install firefox" could work.
edit: https://wiki.debian.org/Firefox
unfortunately not, I got this in reply E: Could not openlock file/var/lib/dpkg/lock - open (13: permission denied)
E: unable to lockthe administration directory (/var/lib/dpkg/) are you root?
liam@kanotixM2N:~$
I should be root: I signed in with my root password.I am as far as firefox-53.0.tar.bz2 in my iceweasel downloads and downloads folder

You would need to do that as root -- so either preface it with sudo if you have it set up or su - to root.
Another edit: Sorry -- you should probably use apt if you're using testing or Sid, rather than apt-get.
further edit for link https://wiki.debian.org/Root