Hi
For the 1st question , as i understand you would like to remove the menu position so you have more space for menu items .
Follow the suggestion given here .
to remove category menu position .
To disable the off-canvas menu , Go to template options and disable it .
Here is documentation for Menu system .
To decrease the menu item size
Go to /templates/ja_megastore/css/custom.css file and add below code
.navbar-default .navbar-nav > li > a {
font-size: 13px!important;
padding-left: 30px!important;
padding-right: 30px!important; }
change the value in the above code to reduce size and padding space in the menu items .
If custom.css file is not present kindly create it .