Change Primary Key / Data In Related Table

I am new to access 2010. I need to change the primary key in a table ("stations", Primary key is "station number"), because future entries will result in double entries for this primary key.

I have another table ("species&stations") which has records of Species for each "station number".

So I created a new Primary key for the "stations" table, now called "species id", being a bit better in defining a unique station (as it contains the year and the species number, i.e. "451_2010")

Now the table "species&stations" references/(is in relationship with) the old primary key, identifying a station number for each record.

How do I get it to recognise the new primary key from the "stations" table, and keeping the records (over 1000...) with all there info.

Approach so far: I tried to create a new field in "species&stations", which should look up the new primary key from "stations" and then autofill the field. i did not manage this though

I attached a screenshot to make the relationships more clear!