Yes you can!
First step: Full Backup of your Server!
Second step: carefully reading of Errata-Files for 1.3, 1.4, 1.5!
If you use Plugins from this site, keep in mind, that you have to read also there descriptions!
In my opinion it’s the best to Update to latest stable 1.3 Version and then directly to 1.5 = https://i-mscp.net/index.php/T…1-3-16-to-1-5-1-Debian-8/