uploading big images.

Hi, me again. I need to tell you that im completely new in LAMP, so please don´t get tired with my silly questions :-). I was able to upload and create thumb images with the same size. But now, I am realizing that I can´t upload images bigger than 1 MB, I don´t know why. I load the image through the upload image.php, then I check it with the check_image.php file, and then, I show the result in the browser with the Show image file, but as I told you, only works with files less than 1 mb. With bigger images, I only get a blank page without any errors. I think it is a PHP.ini file configuration or something. Can you help me? Thanks in advance.