This can be done with the php.ini file. Here is how you do it

Create a file under public_html and name it php.ini ( if you do not have one yet. )  Put the following in it

upload_max_filesize = 5M
post_max_size = 5M

Replace the 5 with whatever size you want. If you are letting other people
upload, a size cap protects your storage space from abuse/overuse.

You will then need to add this line to a .htaccess file:
(Please replace "yourusername" with your cpanel user name an add to the end of the comand line the folder(s) to the location of the php.ini file - Also there is a space between path and /home)

suPHP_ConfigPath /home/Yourusername/public_html

You are more than welcome!

The suPHP_ConfigPath /home/Yourusername/public_html line can go before that or after, should not matter as long as its on its own line. Also make sure your replace Yourusername with your account username.