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No installation necessary for CandidATS 3.0.0 Beta to Stable. Uploading the files are enough.
On Migrate,
1) Backup database, attachment directory, upload directory and config.php
2) Remove all files from the root directory
3) Upload the CandidATS files
4) Restore the attachment and upload directories after migration
Migration to CandidATS 2.0.0 Stable
1) run the {candidats Installation url}/migrateextrafield.php
2) Execute the generated extrafield.sql in the database...