Is there anyway to copy my family tree that is held online, eg back it up to disc or get a copy of the file that i can open up on my computer without always having to be online to use it?
When you are viewwing your tree, go to the part at the top where it says "manage trees". You have to actually be viewing your tree to see it. There you can export it to a gedcom, which will put in on your computer. You need some sort of program which will accept it and be able to read it. myheritage has Family Tree Builder which you can download to your computer.
