"raw value keep time" is the actual values collected if you set it to 10 days then your graphs will show exactly what was collected for 10 days...
Is there a way to edit these settings in version 3.6?
DOH I thought you meant edit the values. I don't remember what it looked like in 3.6 but check the chart tab under settings. NOTE Be careful trying to keep too much raw data it will create a huge database and if the database reaches 2GB it will crash.
Previous post (still good information)
Yes. add the graph you want to modify to a chart, go into the chart and go into the properties of the graph and then advanced somewhere in there is a view of all the collected values, you can look for your "incorrect" value and delete it or just delete all the values and the graph will be empty. Also if you just click Copy for any object the values are cleared. Unfortunately it is not in 4.