When you upload some big size file or install theme/plugin in the WordPress admin panel, maybe you will meet the issue:
The uploaded file exceeds the upload_max_filesize directive in php.ini.
By default, maximum upload size in WordPress ranges from 2MB to 150MB depending on the settings of your web hosting provider is giving by default.
To check what is the current max upload size limit in your WordPress site then navigate to WP Admin / Media / Add New. You will see the current max upload size on the bottom as shown in the screenshot.

There are many ways you can increase the max upload size in WordPress.
php.ini
This is a default file used to configure any application which runs on PHP. This file contains parameters required for file timeout, upload size, and resource limits. Access your WordPress root directory using SSH or FTP and look for a php.ini file. In some cases, this file is not visible to the other option would be to create a new file instead.
Open any text editor and create a new file. Copy the following code and save it as php.ini.
upload_max_filesize = 32M
post_max_size = 64M
memory_limit = 256M
How to Change PHP Settings on Godaddy?
How to Change PHP Settings on SiteGround?
How to Change PHP Settings on DreamHost?
.htaccess
If you don’t have access to PHP.ini try adding this to an .htaccess file.
If your web server is using Apache and PHP is set as an Apache module, then you can add a few lines of code in your WordPress .htaccess file to increase the max upload size in WordPress.
To access your .htaccess file, connect to your server via FTP client and navigate to the folder where WordPress is installed. Open up .htaccess file in a code editor or Notepad and add the following lines.
php_value upload_max_filesize 32M
php_value post_max_size 64M
php_value memory_limit 256M
php_value max_execution_time 120
php_value max_input_time 60
This will define the max upload size in Megabytes. Replace the numbers as per your requirement. The max execution time and max input time are in seconds. The execution time defines the limit of time spent on a single script. Choose a number that is suitable for your site.
wp-config.php File
Another way of increasing the upload size in WordPress is to define the size parameter in the wp-config.php file. To do that, access your WordPress root directory using SSH or FTP and locate a wp-config.php file.

Open the file in any text editor and add the following code.
@ini_set( 'upload_max_size' , '20M' );
@ini_set( 'post_max_size', '13M');
@ini_set( 'memory_limit', '15M' );
Save your changes and it should increase your file upload size.
Increase Upload Size in Multisite
If you are running WordPress multisite, then upload size can be increased from settings. This increase is dependent on your server settings. If your server is set to 20MB you cannot increase WordPress upload size to 25MB. However, if your server is set to 20MB your network setting is set to 15 MB then you can resolve the issue by increasing the upload size to 20MB.

Plugin Method
Not everyone is a fan of writing code or accessing root files using SSH or FTP. For that situation, the plugin comes in handy and luckily there is a WordPress plugin available for increasing WordPress upload size. The plugin we will be using is Increase Max Upload Filesize plugin.
Go to your WordPress Dashboard / Plugins / Add new, search “Increase Max Upload Filesize” then activate and install the plugin. Once installed, go to plugin settings and simply enter the value for upload size.
Note: This guide is written to provide all possible solutions. However, some may not work on the majority of the web hosts. In this case, the best solution is to contact your hosting provider.