As the title describes that sometimes you can can not upload a larger file using the wordpress media uploader. PHP has several configuration options to limit resources consumed by scripts. By default, PHP is set to allow uploads of files with a size of 2MB or less. This is common problem users face and this can be fixed by editing your server’s php.ini file. If you don’t know what exactly to do about editing php.ini file then you should not do it by your own and ask your server administrator.
Try increasing the following values in your php.ini file, for example:
memory_limit = 99M max_execution_time = 300 upload_max_filesize = 20M post_max_size = 24M
If the upload_max_filesize is larger than post_max_size, you must increase post_max_size so that it is bigger than upload_max_size.
If the value of post_max_size is larger than memory_limit, you must increase memory_limit so that it is larger than post_max_size.
Hope it helps.