If the question is, "how do i convert the data to annual the easiest possible way?", the answer is to import using readtable (Check!) then convert using table2timetable and call retime with 'yearly' as the new time basis. I guess you want to get the last value in each year, or interpolate; I don't thnk you want to aggregate in the sense of sum. So something like
ttAnnual = retime(ttMonthly,'yearly','lastvalue')
but I'm just guessing. The I guess you'd lag that, divide the original price by the lagged price, and log.
I believe that the Financial Toolbox has a function called tick2ret, if you have access to that.