To force a collection to run now you use the following steps.
Admin Settings > Data Collection >
At the top un-check Enable Data Collection for this Data Source
Then click save,
Open the collection again check the enable check box and click save again.
This will force the collection code to run again but you may see the status of "All information was collected in a previous run" for some items meaning it will not gather that data again until the next day.
Some collections like "Exchange configuration" and "Lync "Configuration" are both collected using a daily snapshot. If they have already successfully finish today then they will not collect new data until next day(at UTC midnight).