I can’t edit my photos using the default photo library app on my iPhone eg I can’t crop by moving the lines

Edit your photo or video

After you take your photo or video, open it in the Photos app and tap Edit. Then you can adjust the crop, angle, light, add a filter, and more. Choose an adjustment, like Brightness or Saturation, and slide to change the strength and intensity. If you don’t like how your changes look, tap Cancel and revert back to the original.

Adjust light and color

Improve the exposure, saturation, highlights, warmth, tint, and more of your photos and videos. Then use the slider to make precise adjustments with each setting.

Apply filters

Tap one of the photo filters to give your photo a different color effect, such as Vivid or Dramatic. Or try classic black and white looks like Mono and Silvertone.

Crop and straighten

You can drag the corners of the grid tool to set your own crop, then move the wheel to tilt or straighten your photo or video. You can also rotate or flip your photo or video, and adjust the vertical and horizontal perspective. 

Can you post an example of what the "lines" are you are hoping to remove? While you can do basic photo editing using the controls in the editing tools, you may find situations where a more robust photo editing suite may be required. I use Adobe Creative Cloud for more complex editing needs.

I still don't understand what you mean by remove the edges of the picture? Is this a picture you took with your iPhone or one you downloaded from somewhere else?