Hello,
Your queries have been answered below,

1-How can i remove page titles from header of page.
You can see on image.

To remove the page title please go to

Dashboard -> Appearance -> Customize -> Theme Options -> Advanced Options

h1.entry-title {
    display: none;
}

2-How can i change menu color for opened pages.I changed hover color but color for active pages not changing.

To change the active and the hove color, on the same place add the below given CSS

.main-navigation li a:hover, .main-navigation li.current-menu-item > a, .main-navigation li.current_page_item > a, .main-navigation li:hover > a {
    background: #00b9eb;
    color: #fff;
}

Hope it helps.
Best regards.