alon279,
To Change the camera’s video recording settings on iPhone you can go to Settings > Camera > Record Video.
To find out which format Instagram accepts, you'll need to check with the app developer. Here's how to do this:
1. Open the App Store on your iPhone, iPad, or iPod touch.
2. Search for the app, then tap it. If you can't find it, tap the account button
or your photo at the top of the screen, tap Purchased, tap "Not on this [device]," then tap the app.
3. The app's product page appears. Scroll to the Ratings & Reviews section, then tap App Support. If you don't see App Support, make sure that you're signed in with the correct Apple ID.
This information is from How to contact an app developer.
When you upload videos to Instagram, the minimum resolution is 720 pixels. More information can be found here: What are the video upload requirements for videos on Instagram? | Instagram Help Center
Cheers.