This is what I do.
If you haven't already, download Winrar.
In your blockland folder, create a folder called release. In there, make a folder called whatever you want to name your map. In there, make a base folder, in that, a maps folder. Place your .mis, and, if you map has any, the .ter's, .dif, and any additional textures. So it will be like
Blockland
Release
Mapname
Base
Maps
map.mis
map.ter
Then right click on the Base folder inside the Mapname folder, select Add to 'Base.rar'. When it's done compressing, rename Base.rar to something else, and upload.