The file upload size limit is usually set pretty low by shared hosting providers. Why? To save bandwidth, keep the server moving quickly, and think about it -- how many customers really need a large upload limit? If you do need to increase the maximum upload limit, all you need to do is place the following code snippet in your php.ini file:
file_uploads = On upload_max_filesize = 10M //needs to be in {x}M format
Note that not all hosting providers allow customers to increase the file upload limit. Take that into consideration when purchasing your customer's web hosting.