When loading samples you are always given a choice of WHERE to load these samples.
when you get to the stage that says LOAD THIS FILE in a designated section of numbers -
usually 200-299 or 300-399 and so on...
you must look at the soft button options which are

OVFILL > OVERWRT > MERGE > APPEND > FILL > CANCEL

you will want to use APPEND if you want Add samples to your existing sample base
if you just choose OVfill or OVerwrt, it will erase all of your previous data