My Mac will not update, every time I press software update and tick the mac software update it starts to load and update but then it just stops and doesn't move. I have to shutdown the computer which cancels the update. Please, if anyone knows what to do I would really really appreciate it.
As Nick suggests, make sure you give Software Update enough time. The progress bar for checking updates does seem to freeze for several seconds with me, but it gets there eventually.
If you mean the progress bar for installing updates, you should not force your computer to shut down in the middle of a system update. If you do so, you can end up with your operating system in a non-functional state, and need to re-install it from the System Restore disk that came with your Mac. In the worst case, if you do it when it's in the middle of flashing firmware, you can render your Mac almost totally un-bootable. If the install doesn't offer a cancel button, just leave it to do its stuff. Only once no progress has been made for several hours should you consider a force shutdown.
More positively, if you're having trouble with Software Update, you can download the software updates manually from http://support.apple.com/downloads/ with your favourite web browser. Once they're downloaded, simply double-click to install them. The same caveats about aborting midway through an install still apply, however.