Apart from upload_max_filesize you should also increase post_max_size accordingly. Also, max_input_time and max_execution_time might need to be increased for the upload and processing to finish.

It also depends on your server configuration, if you can adjust these php variables via .htaccess at all. You can check the current values of upload_max_filesize and post_max_size on the server info tab in the admin section of your site (Elgg 1.8). If the values don't change when you adjust them in .htaccess, you need to set the values in php.ini of your server config.

You may check your current configuration at admin panel:

Administer->Statistics->Server info

There are values for "POST maximum size" and "Upload maximum size". Minimum is your max possible file to upload as iiony mentioned.

I'll check, thanks for the replies so fast