Subversion clients store authentication data in ./subversion/auth for each realm.

To remove cached data go to “.subversion/auth/svn.simple” folder and delete the particular file.
There will be key (K)-value (V) pairs. “username” and “svn:realmstring” together can identify the user.
So use for example:

grep servername ./*

to find the right file.

Disable caching by opening “config” file in “.subversion” folder and setting the values of “store-passwords” and “store-auth-creds” to “no” or use –no-auth-cache as command line argument.