svn co https://svn.r-project.org/R-project-web/trunk R-project-webto get the pages. Follow the instructions in README.md to make changes and preview them. All changes in the repository are synced to www.R-project.org in Vienna daily at approx. 6am and 6pm CET (=GMT+1).
The only exception is the subtree www.R-project.org/nosvn which contains some automatically generated parts or files maintained by non-R-core members.