As of how to watch there isn't a specific way since there is no correlation between the arches. Which means that you can watch any arch in any order and not get lost. However I do think it is better to watch in order of release to get a full view of how much the saga evolved.

As to where to watch:

HIStory 1: My hero/ Stay away from me/ Obsessed

You can find it on VIKI for free with English subtitles under the title HIStory 1. Each episode is a different arch in the order presented above. (https://www.viki.com/tv/35898c-history-1?utm_campaign=container_share&utm_source=unified&utm_medium=share_button_android&utm_term=35898c&utm_content=social-post)

HIStory 2: Right or Wrong/ Crossing the Line

You can find it on VIKI for free with English subtitles under the title HIStory 2. The first 4 episodes are from the RorW arch while the last 4 are from the CTL arch. (https://www.viki.com/tv/36096c-history-2?utm_campaign=container_share&utm_source=unified&utm_medium=share_button_android&utm_term=36096c&utm_content=social-post)

HIStory 3: trapped 

You can find it on VIKI for free with English subtitles under the title HIStory 3: trapped. (https://www.viki.com/tv/36410c-history-3-trapped?utm_campaign=container_share&utm_source=unified&utm_medium=share_button_android&utm_term=36410c&utm_content=social-post)

HIStory 3: Make our days count 

You can find it on VIKI for free with English subtitles under the title HIStory 3: Make our days count. (https://www.viki.com/tv/36748c-history-3-make-our-days-count?utm_campaign=container_share&utm_source=unified&utm_medium=share_button_android&utm_term=36748c&utm_content=social-post)

and also at caravan youtube channel