First, you can check by going to the menu button on the top right of the browser (the “hamburger” button), then selecting “Settings.” On the right side of the resulting screen, select the “About” option and then you can see the version you are using. It will say either 32-bit or 64-bit in the description.
If it is the 32-bit version and you want to install the 64-bit version (and you have a 64-bit version of Windows), just go to the Chrome download page and install the browser. It will automatically install the 64-bit version. https://www.google.co.in/chrome/browser/#eula