Upgrading and need to buy parts

Here’s the IFIXIT RAM upgrade kit for your system iMac Intel 27" (Core i3) EMC 2390 (Mid 2010) Memory Maxxer RAM Upgrade Kit and here’s the guide to do it iMac Intel 27" EMC 2390 RAM Replacement

While a bit harder to do I would recommend installing the SSD as a second drive Vs swapping out your current HDD. Review this IFIXIT guide to do this Installing iMac Intel 27" EMC 2390 Dual HDD or SSD Drive Here’s the needed tools & cables iMac Intel 27" (Mid 2010) Dual Hard Drive Kit and here’s the needed SSD Crucial MX500 250 GB SSD In this config you don’t need as large a SSD as you are still leveraging your HDD for the deeper storage.

While easier to do, swapping your current HDD is the other option. You do loose the deep storage your HDD offers so you’ll need to think about the size of your SSD depending on how much you are planning to store on it. Review this IFIXIT guide iMac Intel 27" EMC 2390 Hard Drive Replacement and you’ll need this tool kit and this kit also includes the SSD drive iMac Intel 21.5" and 27" (Late 2009-Mid 2010) SSD Upgrade Kit I would strongly recommend going with either the 500 GB or 1 TB drives.