If you are on a shared hosting provider there’s a good chance you will not be able to change it yourself. From the book “WordPress Bible” Part 1 page 22 says:
For optimal WordPress performance, edit your php.ini file (usually located at /etc/php.ini on Linux servers) and set (edit) the configurations to match those shown here:
memory_limit = 8M
upload_max_filesize = 8M
display_errors = Off
If you don’t know where your php.ini configuration file is, you can create a small PHP configuration file on your site. Call it phpinfo.php, type <?php phpinfo()?>, and save the file. Load it into your browser and you should see a descriptive configuration page describing your PHP setup, as shown in Figure 2.1. The location of the PHP configuration file is listed under Loaded Configuration File.
Here’s an old article I found on it as well: https://andrewapeterson.com/2008/04/maximum-file-size-for-uploads-in-wordpress-25-1and1-web-hosting/