You can prepare for the switch on by going over to the PS3 site and downloading the new 3.61 firmware to your computer and transferring it over to your PS3 via USB. In my experience this process tends to be a lot faster than downloading it direct to your PS3. Get it here. Once you have it you need to ensure you have a USB drive with around 200 mb of spare space that is formatted as FAT32. Create a folder called PS3 then a subfolder called UPDATE and put the newly downloaded file in there, eg:
Head on over to the System Update option on the Settings field (va the XMB) and update the system via the USB storage device. This should take about 45 seconds. And that's it. You can try signing in to PSN network to change your password but, currently, it appears to be still undergoing maintenance in the UK as I type. There are instructions for how to change your PSN network password here.