follow these steps:

1. backup your database and installation folder
2. check your backup, that restore is working
3. make a copy of your old web.config
4. prevent access to the old site, e.g. by adding index.html and set index.html as default document in IIS web settings
5. remove all exisiting .vb files
6. upgrade your old site to 4.3.5 by copying all files over using the install or upgrade package (upgrade does not upgrade core modules to new versions)
7. rename release.config to web.config and transfer connection string (twice!), encryption keys and objectqualifier from old web.config to new one
8. in IIS web settings switch to ASP.Net 2.0
9. run default.aspx to execute upgrade script and text your site.

now you are able to transfer your site to new server.

1. new server shall have same modules installed as old one
2. copy web.config, and folders /config, /app_globalResources and /portals as well as all folders with child portal names.