It is sort of confusing.
First of all, there is no option that says "Dedi" yes or no, so you have to do it manualy.
Ok, first, open up your Blockland Folder in C:/Program Files/Blockland and look for somthing that says dedicated.bat
Right click it and hit rename. Change the file extension (the three letters after the period) to txt
so it will look like dedicated.txt.
Open it and type pause.
It should look like this
start blockland.exe -dedicated -map construct (or any map)
pause
Change it back to .bat, and run it. After it finishes, it should show up with somthing saying RTB, (If you have RTB 2.1 Do what it says, wait, then start blockland and join your server.