Upgrading your Debian VPS from Wheezy to Jessie

Just follow the regular Debian apt-get upgrade, dist-upgrade, reboot process:

https://www.debian.org/releases/jessie/i386/release-notes/index

Big changes are:

new apache directives eg Require all granted. and locations conf-available, conf-enabled etc. conf.d is ignored. 
Cyrus executables have moved so use maintainer cyrus.conf. 
Important samba global "acl allow execute always = yes" to allow files to be executed as per all previous versions of samba