WordPress 301 redirection from subdirectory installation to other subdirectory

.htaccess

# The following code will not only affect the subdirectory itself but all content within!
# Add it to the top of your .htaccess file BEFORE WordPress´ own rules, starting with "# BEGIN WordPress"

# Move from "old"-directory to "new" directory
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteRule ^old/(.*)$ /new/$1 [R=301,L]
</IfModule>

# In case you want to move from a subdir to the root-directory just remove the "new" from the second parameter like this:
# RewriteRule ^old/(.*)$ //$1 [R=301,L]