Windows 8 32bit to V 64 bit

Hello

I have an Inspiron 1525. 64 bit system. It came with Vista onboard directly Dell. 

I purchased Windows 8 Pro disk from the local shop and foolishly installed the 32 bit version on the laptop by mistake. (Which luckily works fine) 

I want to take off the 32 bit and install the 64 bit version of the OS but Windows 8 does not seem to let you change between the two.

Assuming I have already backed up my files using the 32 bit version of the Windows 8 "File history" app what is the best procedure I should use to get to be running the 64bit version and maximise the potential.

Thanks, Alan