What action should you take if Windows shows less than 4 GB of memory available after installing an OS on a 64-bit system?

When a 64-bit operating system is installed, it is designed to utilize more than 4 GB of RAM, as 64-bit systems can address significantly larger amounts of memory compared to their 32-bit counterparts, which are limited to just under 4 GB. If Windows is showing less than 4 GB of memory available, the likely reason is that a 32-bit version of the operating system has been installed instead of a 64-bit version.

Installing a 64-bit version of the operating system will allow the system to recognize and utilize the full capacity of the installed RAM, assuming that the hardware supports it. Thus, if the system is equipped with more than 4 GB of RAM, correctly installing a 64-bit OS is crucial to taking full advantage of that resource.

The other options do not address the root issue. Upgrading the RAM would be unnecessary if the installed memory exceeds what’s visible, and changing the RAM configuration in BIOS wouldn’t resolve the limitations imposed by having a 32-bit operating system. Using a different video card does not affect the operating system's ability to recognize system RAM. The proper resolution involves confirming and ensuring the correct version of the OS is used.