The first thing you need to do is to determine the type of RAM modules compatible with your PC. Consult the manual that came with your PC motherboard to learn of the RAM modules that you need and how they are to be installed. There are several RAM modules available in the market, namely DDR, DDR2 and DDR3. The motherboard manual will help you decide which of the three modules you will be purchasing. It is also important to keep in mind that new PCs commonly use dual-channel memory, which means that you will have to install two instead of one new RAM module. Again, consult the manual to know if your PC uses dual-channel memory.
Once you have determined the flavour of RAM that is best for your PC, visit a computer shop and make the purchase. Buy two instead of one RAM modules if your PC uses dual-channel memory. Be sure to ask the shop-keeper for a warranty as you may want to get them exchanged in case the modules turn out to be faulty.
Once you have the RAM modules, it is time to install them on your PC. Shut down the computer and unplug it from the socket.
Carefully remove the side covers of the CPU (central processing unit). You may need to use a screw driver for the purpose of removing the covers. Some PC casing can conveniently be removed by unhooking them and sliding them open.
Once the covers are removed, look for the RAM slots on the motherboard. If you have trouble locating them, use the manual that came with the motherboard to help you find them.
If there are free slots, carefully insert the module into the slot. As the module is notched, it will only fit into the slot in a single direction. If it is not going into the slot, do not use force to push it in as you will end up damaging both the RAM and the slot. Once the RAM is inserted in the slot, hook it in its place with the plastic or metal retention clips. If they are no free memory slots, remove the RAM already installed by prying apart the retention clips and inserting the new RAM in its stead. Remember to insert the second RAM as well if your PC uses dual-channel memory.
Put the side cover of the CPU back on. Now put the plug back in the socket and power on the PC. Your system will automatically recognise the newly installed RAM.