If you have customized the plugin slightly, e.g. changed css a little or made some slight code change, you can update BUT before that please make backup to save the changes you have. If you customized the plugin via child plugin, you can make update right away. Please, note, that the update can be done within major plugin version.
If you ordered customization service from Estatik team and our developers made custom work, you can update without any issues within major plugin version the customization was done for. We do customization in the child plugin and i doesn't intefere with the core plugin.