Detailed community post: https://designspark.zendesk.com/hc/en-us/community/posts/115000087525/comments/115000034185
Based on a suggestion from our community member 'Rob Eaton':
The resolution for the mesh can be set in
File -> Designspark Options -> File Options -> STL.
The Deviation and Angle can be changed.
You can also get to this on the 'Save As' Window in Options.
As you can see in the image from left to right.
Coarse - Medium - Fine - Custom
The Custom setting in this case is- Deviation 0.25 - Angle 2°