Xynk allows you to customize just about every aspect of your data graphs, and there are multiple and redundant ways to tweak their appearance.
Be sure to check out the many How To animated help items for tips to handle the most frequently graphing solutions, available on this site or via the Xynk in-app Help menuSection 2 of this Guide goes into great detail on all the controls for graph formatting. To summarize here, you can change a graph through:
You can show the inspector side panel with the Inspector button of the tool bar.