Before using virtual RAM or free RAM cleaner software:

The “download more RAM” joke dates back to the late 1990s and early 2000s, when dial-up internet was slow and RAM was expensive. Back then, upgrading from 64MB to 128MB could cost over $100.

While you cannot download physical RAM, you can allocate a portion of your hard drive or SSD to act as (also called a page file or swap memory). This tricks your computer into thinking it has more RAM than it physically does.