How do I create a step in my SQL Server Agent Job which will run my SSIS package?

I'm trying to create an automated job for the SQL Server Agent to run. The job is supposed to run my SSIS package.

Here's what I have so far:

EXEC sp_add_job @job_name = 'My Job'
            ,@description = 'My First SSIS Job'
            ,@job_id = @jobid OUTPUT

EXEC sp_add_jobstep @job_id =@jobid
                    ,@step_name = N'Upload Data'
                    ,@step_id = 1
                    ,@command=N'/FILE "D:\Installs\Upload.dtsx"'
EXEC sp_add_jobstep @job_id = @jobid
                    ,@step_name = N'Download Data'
                    ,@step_id = 2
                    ,@command=N'/FILE "D:\Installs\Download.dtsx"'

Unfortunately when I run this, I get an error saying

Incorrect syntax near '/'

I suspect it's complaining about the /FILE in my command.

I can't find documentation about the appropriate syntax to use within @command anywhere -- I pulled /FILE out of some old code I found somewhere. What is the correct syntax for running an SSIS package in a job?