In v3.x the migration was part of the installer, however we realized that this caused problems because the installer runs as administrator and in order for the migration to work correctly it needs to run as the user. In addition the migration was intended to migrate settings from v3.4 and below to the new default location set for v3.6.
With the new 4.0 installer the whole migration process was removed because it was no longer needed and didn't function in a way that made any sense.
When running the 4.0 installer it doesn't look for your previous v3.x installation, it uses the default configuration placing the data files in the all user application data folder or if using a per-user installation the user application data folder.
The first time FlashFXP 4.0 is started it tries to detect a previous v3.x installation and if found it prompts the user to import the v3.x settings to the new data folder.
Assuming FlashFXP is able to detect a previous v3.x installation everything will import and work flawlessly.
For a few users where the registry keys for their v3.x installation are missing or corrupted we suggest using the backup / restore feature in FlashFXP. By backing up FlashFXP v3.6 from within the application and then restoring the backup within FlashFXP v4.0. We have a guide explaining the backup / restore procedure located
here.