Help with replacing values.

I have a list of text values each have a category number i.e

Col1 || Col2
1508 || John Smith
1508 || Jane Doe
1509 || John Doe
1509 || Jane Smith
1510 || Robert Smith

And another two columns relating the category number i.e.

Col1 || Col2
1508 || Solicitors
1509 || Teachers
1510 || Drivers

I have 30,000 names and 1500 categories.

I need my sheet to end up like this:

Col1 || Col2
Solicitors || John Smith
Teachers || John Doe

So I need to search i.e "1508" and replace it with the text associated with it.

I know it can be done with search>replace all but I have 1500 categories... I need something automatic!

Can anyone help me with this?

Thanks in advance!

Ray