how do I change my startup menu?

One place is System Preferences -> Users & Groups -> Login Items

If you have installed 3rd party additions that run as Launch Agents, Launch Daemons, and/or kernel extensions, then those would require you to use the vendor's uninstall instructions, or get down and dirty with something like EasyFind to search and destroy.

For these 3rd party items, EtreCheck will at least list them for you

<https://discussions.apple.com/docs/DOC-6174> or <https://etrecheck.com>

If you with the forum to look over your 3rd party items and give recommendations, please post the EtreCheck output

If, when trying to post the output, you get the error:

"The message contains invalid characters"

then try posting to PasteBin.com, and give us a pointer.

<http://pastebin.com/>

What do you mean by your Startup menu? Are you saying Apple menu -> System Preferences -> Startup Disk is not showing all the bootable disks you desire?

The list of programs that start automatically each time the mac is booted. They usually run in the background.