There's no such option.

How do I answer delete in my script when I get the message "Error message from server: Permission denied
(D)elete, (A)bort, (R)etry, (S)kip, Ski(p) all: Abort". I don't see an option for batch that would choose delete?

Here is example session

C:\Users\blah\Desktop>winscp.com /script=WINscp.txt
batch off
confirm on
Searching for host...
Connecting to host...
Authenticating...
Using username "blah".
Authenticating with pre-entered password.
Authenticated.
Starting the session...
Session started.
Active session: [1] blah@blah.com
/var

Using configured transfer settings different from factory defaults.
C:9999999999999999.ipg | 0 B | 0.0 KB/s | binary | 0%
Cannot overwrite remote file '/var/tftpboot/9999999999999999.ipg'.
Permission denied.
Error code: 3
Error message from server: Permission denied
(D)elete, (A)bort, (R)etry, (S)kip, Ski(p) all: Abort
Session 'blah@blah.com' closed.
No session.