Thanks devinemke but I can't do that, since I am using shared hosting and as such I do not have direct access to the php.ini file. I tried using the following code:
if(!ini_set('post_max_size', '60M'))
echo "can't change the php.ini file!";
if(!ini_set('upload_max_filesize', '8M'))
echo "can't change the php.ini file!";
if(!ini_set('memory_limit', '61M'))
echo "can't change the php.ini file!";
But I get that 'can't change the php.ini file!' message three times, so it seems the server won't let me... Any ideas?