BL have confirmed that there is no option to increase the file size within the GUI. A workaround has been provided though which works!
1. Export your data source via right click as an XML
2. Open the file in a text editor
3. Improve the value of XML tags '<maxFileSize>200</maxFileSize>' and define the desired size in Kb. I don't recommend to define very huge values as it might cause performance problems :-)
4. Save the file
5. Remove the original data source from the SMP console and import modified data source via right click.
6. Now you should be able to export to a larger file.