I would like to add to what Louis posted regarding a 32-bit version of Windows. A 32-bit Windows operating system has an address space of 4GB. The address space is used for RAM, network, video, hdd, etc. The total amount of memory used for these averages around .5GB, this means that the maximum amount of RAM available is around 3.5GB. Any amount of RAM added beyond the 4GB would be superfluous since it will only recognize 4GB. In order to add any additional RAM you would need to install a 64-bit operating system. You can not convert a 32-bit operating system to a 64-bit operating system, you have to install a 64-bit operating system.
Before you lock yourself in on upgrading to Windows 7 you should download and run the Windows 7 Upgrade Advisor.
It would be helpful if you would post the make and model of this computer.
As previously requested, please download and install Speccy to provide us with information about your computer. Clicking on this link will automatically initiate the download.
The one piece of information the Speccy will not provide is the make and model of your PSU. If you know what it is please post this along with the Speccy link which will be generated.
When Speccy opens you will see a screen similar to the one below.
Click on File which is outlined in red in the screen above, and then click on Publish Snapshot.
The following screen will appear, click on Yes.
The following screen will appear, click on Copy to Clipboard.
In your next post right click inside the Reply to Topic box, then click on Paste. This will load a link to the Speccy log.