You have a few issues here upgrading the RAM to the max 8GB is as high as you can go, and OS-X El Capitan (10.11.6) is as high as this system will go as well. So that limits you on what apps you can run. Small iMovie projects is about the limit. Using your system to host your family pics is workable, but you don’t want to depend on the system drive alone you should have a backup solution just in case.
So that brings us to the last issue your drive upgrade. Your system uses an older version of SATA we call it SATA II (3.0 Gb/s), todays SATA interfaces are SATA III (6.0 Gb/s). So the drive you get needs to be able to run at the slower SATA data rate. Most drives today are fixed speed only able to run at SATA III. Some drives are able to run at the slower speed by matching the systems I/O ports speed (we call it Auto Sense Vs Fixed Speed). So what ever drive you get make sure the spec sheet calls out the slower SATA speeds. As an example: [https://www.samsung.com/semiconductor/global.semi.static/870_Series_Brochure.pdf|Samsung 870 EVO or 870 QVO SSD’s] Note the Interface line lists 3.0 Gb/s (SATA II).
Here’s the guide to replace your current HDD with the SSD [guide|919]