win 8 32 bit to win 8 64 bit

I have upgraded my DELL Inspiron 1525 to win 8 32 bit using an upgrade CD with no problems.
I now wish to upgrade further to win 8 64 bit using the 64 bit upgrade CD.

When I inserted the 64 bit upgrade CD it said 'your current version of windows is 32 bit and does not match the architecture of the 64 bit installation media.'

I am told that my laptop will support 64 bit so why doesn't it allow me to upgrade????

Please can you help?