64-bit Windows has two "Program Files" folders. One has the "x86" at the end. So you definitely have 64-bit Windows.
You can also go into Task Manager (CTRL-ALT-DEL). Under "Performance->Memory" it will show a graph of your System Memory (the DDR3 sticks) and how much is currently being used.
(BTW, Microsoft frequently uses the term "x86" to mean "32-bit" when it means nothing of the sort. "x86" is the general architecture just like Apple used to have "PowerPC" CPU's. It's really "x86-32" and "x86-64" not x86 and x64.
It started when x86 CPU's were 32-bit only so the term was interchangeable, but it's annoying that Microsoft even uses it incorrectly.)