...
If you create a new issue with attachments, all attachments referring to that issue, will automatically be uploaded. However, you can make adjustments to your attachments i.e. you can delete one or more if you do not need them.
...
Uploaded all attachments
...
Deleting one attachment
For deleting an attachment, you click on the relevant document and the blue hook disappears. This attachment will then not be uploaded in your Jira issue.
...