To increase the upload size in PHP you need to modify some variables in the php.ini file on the server. If you don't have access to that file you can override the defaults using .htaccess. If your server uses phpSuExec use the 2nd method. Create or add to the current .htaccess file in the document root directory.

# .htaccess

php_value upload_max_filesize 20M
php_value post_max_size 20M
php_value max_execution_time 200
php_value max_input_time 200

Method for phpSuExec Create a local php.ini in the document root directory

# php.ini

upload_max_filesize=100M
post_max_size=105M
max_execution_time=600
max_input_time=600

Create or add to the current .htaccess file the location of the php.ini file

# .htaccess

SetEnv PHPRC /[path-to-document-root]/