Para alterar DocumentRoot de /var/www/html para /srv/www/html , abra apache.conf e altere:
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all granted
</Directory>
com:
<Directory /srv/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all granted
</Directory>
Salvar apache2.conf e reiniciar o apache:
sudo service apache restart