Add the below to the relevant php.ini file (recommended, if you have access). Note that for some hosts this is a system-wide setting. However, for hosts running PHP as a CGI script with suexec (for example) you may be able to put these directives in a php.ini file in your Drupal root directory
.upload_max_filesize = 10M
post_max_size = 10M
Add the below to your .htaccess file in your root directory.
php_value upload_max_filesize 10M
php_value post_max_size 10M