I am having DDR4 RAM in my laptop. Can I put DDR3 RAM in that.
A laptop that supports DDR4 RAM will not support DDR3 RAM. RAM is not backward or forward compatible. Hence, you need to use the same RAM that is supported by your laptop.
Modern laptops are coming with DDR4 RAM. You can check the specs of the laptop, number of slots available, max RAM capacity by going through the laptop manual.
RAM can be purchased and installed on your own. However, you would need to open the laptop to install the RAM. For some of the laptops, RAM can be easily upgraded by opening a few screws. However, for a few laptops, the process is very arduous and time consuming. You may have to take the help of a specialist to get the RAM upgraded.