You have two issues: 1. First, you must determine if each of your systems is capable to run 64-bit OS. That means determining if you have a 64-bit capable CPU. You didn't tell us your CPU, or I would have looked up the information for you. But, you can check yourself. I don't have Windows 7 in front of me, so I got these instructions from Microsoft. If it's not exact on yours, you should be able to figure it out. Select the Start button, and then select Control Panel. In the search box, type Performance Information and Tools, and then, in the list of results, select Performance Information and Tools Select View and print detailed performance and system information. In the System section, you can see what type of operating system you're currently running under System type, and whether or not you can run a 64-bit version of Windows under 64-bit capable. If each says 64-bit capable, that means that each of your PCs is able to run 64-bit Windows. That means that you would be able to install more RAM, and then perform a new clean install of Windows 64-bit. You should then install Windows 10 64-bit, and I will explain why in my next point. 2. Windows 7 is unsupported and insecure. It does not receive security patches, so it should no longer be used on a PC connected to the Internet. I suggest that you update to Windows 10. Do the free upgrade: [URL] After upgrading, check to see if Windows 10 is activated in Settings | Activation. If it is, then you can perform a clean install of Windows 10 and it should activate automatically. So, after you upgrade to Windows 10, if each system is 64-bit capable, then you can install the extra RAM and then perform a clean install of Windows 10 64-bit. Another method, which does not require you to first do the upgrade to Windows 10 32-bit: install the RAM and then perform the clean install of Windows 10 64-bit, and at a certain point in the process when asked for a product key, you enter the Windows 7 product key. This usually works. If you no longer have the Windows certificate of authenticity sticker with product key, you can find the product key with a free utility such as NirSoft ProduKey. Even if you discover that your systems are not 64-bit capable, you should still move to Windows 10, since Windows 7 is such a huge security risk. Regarding the clean install of Windows 10, there is more detail in a post that I made: [URL]#M2
I fear the logical answer may be to simply go out and buy a newer computer!!  However, I have a nicely running Dell Inspiron 530 as well as an Optiplex 760.     Both are using 4Gb of RAM (but with only 3.2 Usable). Both are 32-bit systems, and I would like to add more RAM to at least one as they are both fairly slow machines!, but that means going to a 64-bit upgrade as they apparently can't handle more RAM as they are. So the query is - am I just making work for myself or is such an upgrade fairly easy please?
Upgrading computer Windows 7 from 32bit to 64bit