All releases of RStan back to 1.3 are available from

• All RStan Releases

This approach will work to (a) update the version of Stan to a newer version, (b) downdate the version of Stan to an older version, or (c) reinstall the same version.

To update, downdate, or reinstall RStan, youMUST:

1. uninstall current version of RStan
2. quit R
3. restart R
4. install new version of RStan
5. quit R
6. restart R

Full instructions are part of the guide to

• Getting Started with RStan

The easiest way to do it is to install 1.3 to a different directory. By default, it will install to the first directory given by

.libPaths()

which looks like

[1] "/opt/site-library"             "/usr/local/lib/R/site-library" "/usr/lib/R/site-library"      [4] "/usr/lib/R/library"

Then

install_url('https://github.com/stan-dev/rstan/releases/download/v1.3.0/rstan_1.3.0.tar.gz', args = paste0("--library=", .libPaths()[2]))Downloading rstan_1.3.0.tar.gz from https://github.com/stan-dev/rstan/releases/download/v1.3.0/rstan_1.3.0.tar.gzInstalling package from /tmp/RtmpJLwfA3/rstan_1.3.0.tar.gzInstalling rstan

You need to make sure that you have write permissions for the folder you are trying to install to. Then to use, for example, v1.3.0 instead of v2.0.0, you can do

library(rstan, lib.loc = .libPaths()[2])

or wherever you installed v1.3.0. It won't work to have two versions of therstan package loaded at the same time. It will not work in Windows todetach() one version and load the other in the same R session --- you have to restart R.