First you will need to change or add the code to your php.ini file if you have one, if not you can try to change it or add it  in the htaccess file

Once that is done then the value in the oxwall admin for uploads will change and you can select the value you want. 

First see here, 

https://developers.oxwall.com/forum/topic/47341

you will find the section on uploads, remember that i have commented out those commands with ;value    so youll have to remove the leading ; to uncomment the code to make it active. 

Also remember that not all hosts allow you to change php.ini or create local php.ini files, if that is the case you will either need to contact them to modify the active php.ini file for your site or try to change the value via htaccess like so.

php_value post_max_size 30M

php_value upload_max_filesize 30M

you can change the 30 to whatever you want.  Also the htaccess attempt may not work depending on how your host has set up the server. 

If you are on a shared host i suggest you contact the host and ask them how you should do this change regarding the information above. 

:) dave