Is it possible to delete the attachments from the Solution that are already processed?
It is not possible to directly remove from the Process.
However there is workaround that users can perform.
First of all to perform these steps
a) User need to be the Site Admin
b) On the Attachment Control "Allow Deletion" option need to be true.If this option is not True user wouldnt be able to perform the workaround either.
If they have this access then you can perform the below steps.
1) Launch Form from the Sharepoint List
Winshuttle Form Site - List- Look for the form- Show form; below screen will appear.
On this Page from the Attachment XML copy all the data to Notepad++ and remove the attachments user would need to remove ; please keep copy of actual code in any case of discrepancies.
After removing Paste that XML code back in .
Now at the bottom of the screen where it says Attachment on the right hand side of the attachments there will be Delete Button- Click on that to delete the required file.
Click Save and refresh the Page; it should delete the unwanted files.