The single most impactful upgrade you can make is replacing the original mechanical hard drive (HDD) with a Solid State Drive (SSD). A standard 2.5-inch SATA SSD, available in sizes from 240GB up to 1TB, will dramatically increase the laptop's performance. This results in a near-instantaneous boot time and a significantly more responsive system.
The system generally shipped with 3GB or 4GB of DDR3 RAM. One of the laptop's strengths is its upgradeability; it features two accessible slots that can support up to 8GB of RAM. In 2021, upgrading to the 8GB limit is almost a requirement to run a modern operating system like Windows 10 effectively. Graphics and Display sony vaio pcg61211m specification 2021