LyX ⇒ Change bibliography reference style - "et al"

[peytonator]

Hello,

I am using the classicthesis LyX template (http://code.google.com/p/classicthesis/), and was wondering how to change the format of the references in the bibliography? At the moment, the bibliography uses the plainnat style

I want to use "et al." when there are more than 3 authors in a reference.

For example, at the moment, a reference may look like:

[7] H R Dinse, K Krüger, A C Akhavan, F Spengler, G Schöner, and C E Schreiner....

I want this to look like:

[7] H R Dinse, K Krüger, A C Akhavan, et al. ...

Please can you help me make this change?

Many thanks.