Some hosts allow certain changes to the central php.ini file.
If they do then it is done by placing a personal php.ini file on the root directory of your site on the server (using ftp).

I have a file called php.ini on my root which changed several server global php.ini settings.

The file is simply a text file containing the following, and saved as php.ini.

=================content=========
upload_max_filesize = 200M
post_max_size = 200M
date.timezone = Europe/London
memory_limit = 400M
===============================

You could try this and see if it helps.