As it is a major update you have to replace your old files carefully as described below,
Please follow the steps strictly:
1. First of all open your ‘database.php’ file from application > config > database.php
2. Copy your database credentials from “database.php” which are 'hostname’, 'username’, 'password’, 'database’, to a text file which will be needed after some time.
3. Open the project folder which you have downloaded from codecanyon.
4. Extract the project.
5. After extracting, open up your project and copy the ‘application’, 'assets', ‘update_pack’ folder.
6. Replace those copied folder with your existing ‘application’ 'assets', and ‘update_pack’ folder.
7. Now open your ‘database.php’ file from application > config > database.php.
8. Replace the 'hostname’, 'username’, 'password’, 'database’ values by the copied values which you did on step2.
9. Open your ‘routes.php’ file from application > config > routes.php. Move to line number 52 and make your default controller “home” instead of “install”
Now, Login to your application as Admin user and,
- Go to general settings from settings menu in admin panel
- Move to the section 'Update Product' on that page
- Upload the file 'update_5.4.zip' from your copy of ekattor app downloaded from codecanyon inside the “update_pack” folder.
- Hit the button 'install update'
- That's it

PLEASE MAKE SURE THAT YOU ARE RUNNING THE 5.3 VERSION BEFORE UPDATING TO 5.4
IF YOU ARE ALREADY RUNNING THE 5.4 VERSION THERE IS NO NEED TO UPDATE… Thank You