how do you add 2 data sets together

[david]

just wondering if someone might advise me on the correct or most efficient way of adding 2 data sets together

I downloaded some historical data which finishes at end of 2010 for various currencies

I want to copy it in to the history folder of an active account and add this years data to the historical data set

but not sure if this is the right way to go and whether the historical data will be overwritten

your advice would be appreciated

thanks in advance!