Gazebo does not reflect any changes I make in its files

I am currently working on a uav simulation, and I am using Kinetic and Gazabo 7.

I tried changing the world file included in the launch file however it does not reflect the changes when I run the launch file. I even tried changing some parameters in the xacro file, and I also tried changing something in the world file, still, it does not reflect when I run gazebo.

I hope someone could help me with this one.

You probably have the simulation package installed and not only built in the devel space of your workspace. Look either in the install folder in your workspace (if you have any), or in /opt/ros/kinetic/share. A copy of the world file should be somewhere there.