Use the export-import utility to migrate your data from version 3.1 to 3.5.

First, export the existing 3.1 data:

cd <jasperserver 3.1>/scripts
./js-export.sh --everything --output-dir js-data_backup

Then, input the data into 3.5:

cd to <jasperserver 3.5>/scripts
./js-import.sh --input-dir js-data_backup

optionally include --update to replace any matching existing entries