BuddyPress.org

As to your first question:

Look in the loop in your theme’s index.php file for this:

<p class="date"><?php the_time('F j, Y') ?> <em><?php _e( 'in', 'buddypress' ) ?> <?php the_category(', ') ?> <?php printf( __( 'by %s', 'buddypress' ), bp_core_get_userlink($post->post_author) ) ?></em></p>

Make the necessary changes.

As to your second question, look for this also in the same file:

<div class="widget" id="latest-news">

<h2 class="widgettitle"><?php _e( 'Blog', 'buddypress' ) ?></h2>

Change the word “Blog” To whatever you like.

Please note: if you plan on sticking with BuddyPress’ standard themes, you will lose these changes the next time you upgrade BP. So, either you live with that and make the changes again with each upgrade, you create your own custom themes (possibly by simply copying the current themes and renaming them), or you never write over the theme files when upgrading.

The second option is the best in my opinion. But, with each upgrade, you should still evaluate any changes that may have been made in the new standard theme as they could be important.