Since v2.5 is based on a new version of AVS/Express you need to download the full package and update by

1. Rename the existing DLV installation directory, e.g. rename dlv to dlv.old (If you a running a license server it should be stopped, and can be removed)
2. Follow the installation instructions and unpack the new distribution into a directory with the same name as used by the old version of DLV. When editing the $DLV_ROOT/bin/dlv or $DLV_ROOT\dlv.bat file you can use the same settings for most variables that are used in the old version.