I have an old 2008 iMac with a 2.4ghz Intel Core 2 and 6 GB ram currently running 10.6.8.   The hard drive is clicking and is acting like it'll fail any minute.  Someone at the local Mac repair store (clerk not a tech) in my area said that by putting a new SSD drive in it would  make it a candidate for updating to High Sierra.  However, I can't seem to find anything online that backs that up.  Would adding a new SSD really make it eligible for High Sierra?