Firstly - Do you need to retain the Danish version? If not and you have the Win 7 install disk (UK version) Boot from that, format and do a FULL install. Then download and install the Service Packs bearing in mind that all software will have to be reinstalled.
If you want to Dual Boot then here are the instructions for doing so (then remove the Danish version at a later from the boot menu) enter link description here
There's also a way to just change the language pack which I am giving you 2 links to have a look at and for you to decide - I have never used this method so I can't advise any further enter link description here enter link description here