Since version 16.0 we only offer 64 bit versions of Web Designer and Web Designer Premium. The below is legacy information.
Since v9 we have offered a version of Web Designer Premium that takes advantage of the power of 64 bit on Windows 7/8/10, if your computer supports it. This enables you to create larger, more content rich sites, excellent news for anyone creating large sites with lots of high-resolution photos (typically 50 or more) where the memory limits of 32-bit Windows were becoming a problem.
NOTE: in version 9, none of the Live Effects plug-ins that we bundle with Web Designer Premium work with 64 bit Windows, so you will lose the use of these plug-ins (although you can install both 32 bit and 64 bit versions if you wish to still use the plug-ins, but note that you can't run both versions at the same time). This restriction was removed in version 10.
Here's how to find out if your computer is 32 bit or 64 bit:
Windows 7: in the start menu right click on Computer, select Properties
Windows 8.1 or 10: Click on Start > Control Panel > System