How to change the file upload size

There are a few ways to change that. Here are the most common ones.

1. .htaccess File

If the server uses Apache and PHP, there is a possibility to customize this via the .htaccess. 

The file is located in the wordpress installation. 

Simply add the following lines: 

php_value upload_max_filesize 64M
php_value post_max_size 128M
php_value memory_limit 256M
php_value max_execution_time 300
php_value max_input_time 300

Tailor the numbers to your needs. The first 3 lines are for the size. Specified in megabytes. The last two are for execution time. These are in seconds. If you specify 0, it is infinite.