Add data rows based on unique numbers in kolom

Hey,

I got a file with a lot of information (+/- 15.000 rows), this information is added trough a (lets call it temp) file (about 200 rows) which is constantly updated with new rows, information in existing rows and completed rows get deleted.
Now the big file I got is supposed to keep all the information ever been in the temp file so we can make anylises of it and get important data. (except changes in rows, these contain price changes which can be overwritten)
The thing I would like to achieve is that the information from the temp file gets automaticly added to the big file.
For this I created unique numbers in kolom A for every row in both files. (its a calculation between non-changing information in the row which can never be the same outcome for two rows)

Now my idea is this:

I have the temp file open
I Dim kolom A as range
Then I use, for every value in range ***
The 2 lines below define the action they need to do, but I can't find anywhere how to do it
If value in range is existing in kolom a of the big file, copy the entire row with the unique number from the temp file, and paste it over the row with the same unique number in the big file.
elseIf the value from the range is not found in the big file then add the row from the temp file under the existing rows in the big file.

I hope you guys can help me out on this

Thanks in advance