This DH wiki article tells you how to accomplish the upload_max_filesize change, and it really does not get any simpler than that. Also, there are many forum posts that discuss this.
If you need help with a particular part of that process, post back with a specific question and someone may be able to help you over that spot.
As for the post_max_size, the process in this same. You could either incorporate that change into the process described in the wiki article or simply edit the php.ini file you produced with the article to change it "manually"