You can change it in the menu Tools -> Parallel upload count, click on the last option (under 8 ) to set higher value (up to 100). Or just send bug report from program and we will solve it
I use fileuploader to upload my files via my VPS.. but when i choose the parallel upload count, the maximum is num. 2.. I don't know.. because my PC use this app normal.. try to restart my VPS but nothing change