How to modify an R package to create a new package for Reweighted Kernel Density Estimation?

I am working on开发者_开发百科 "Reweighted Kernel Density Estimation". I couldn't find any package in R for "weighted bivariate density estimation. That's why I am going to modify availabe univariate packages. But I don't know how to access to source code for those packages. Please let me know how do that.

All source files can be found on CRAN: http://cran.r-project.org/web/packages/

You are looking for the tar.gz archive.

You can also type the function you are interested in modifying's name into the R console without parentheses. That will give you the code, but most even halfway complicated packages use either S3 or S4 classes/methods, so you'll need to know more about those to extend them properly.