That depends on which theme you use and which pages (item, user profile, registration etc.).
For Bender theme, for example, you can delete them:
item-sidebar.php
<?php if ( osc_user_phone() != '' ) { ?>
<p class="phone"><?php printf(__("Phone: %s", 'bender'), osc_user_phone()); ?></p>
<?php } ?>
<div class="control-group">
<label class="control-label" for="phoneNumber"><?php _e('Phone number', 'bender'); ?> (<?php _e('optional', 'bender'); ?>):</label>
<div class="controls"><?php ContactForm::your_phone_number(); ?></div>
</div>
item-post.php
<div class="control-group">
<label class="control-label" for="address"><?php _e('Address', 'bender'); ?></label>
<div class="controls">
<?php ItemForm::address_text(osc_user()); ?>
</div>
</div>
user-profile.php
<div class="control-group">
<label class="control-label" for="phoneMobile"><?php _e('Cell phone', 'bender'); ?></label>
<div class="controls">
<?php UserForm::mobile_text(osc_user()); ?>
</div>
</div>
<div class="control-group">
<label class="control-label" for="phoneLand"><?php _e('Phone', 'bender'); ?></label>
<div class="controls">
<?php UserForm::phone_land_text(osc_user()); ?>
</div>
</div>
<div class="control-group">
<label class="control-label"l for="address"><?php _e('Address', 'bender'); ?></label>
<div class="controls">
<?php UserForm::address_text(osc_user()); ?>
</div>
</div>
user-public-profile.php
<div class="control-group">
<label class="control-label" for="phoneNumber"><?php _e('Phone number', 'bender'); ?> (<?php _e('optional', 'bender'); ?>):</label>
<div class="controls"><?php ContactForm::your_phone_number(); ?></div>
</div>
<?php if( $address !== '' ) { ?>
<li class="adress"><?php printf(__('<strong>Address:</strong> %1$s'), $address); ?></li>
<?php } ?>
<?php if( $location !== '' ) { ?>
<li class="location"><?php printf(__('<strong>Location:</strong> %1$s'), $location); ?></li>
<?php } ?>
For other themes, you should contact their developer(s) and ask for help. Some themes offer additional fields in e.g. registration pages, etc.
Regards
dev101