If you save K2 article and K2 remove from the Tags spases and dashes - we need fix this in function check (). Open administrator\components\com_k2\tables\k2tag.php. Pleace find line 30 and replase this code

// Oldest line 30
$this->name = JString::str_ireplace('-', '', $this->name);

Replase old line in this code:

// approve - and space
$this->name = JString::str_ireplace('-', '—', $this->name);
$this->name = JString::str_ireplace(' ', ' ', $this->name);

To replace Teg you should run a query UPDATE. First you need to go to K2-> Tags and find out under what id is required tags. Next in phpMyadmin we insert sql query code like this:

-- If we want to replace the tag id 6 wherever there is tag with id 12, the request will be so
UPDATE `you_prefix_k2_tags_xref` SET `tagID` = '6' WHERE `you_prefix_k2_tags_xref`.`tagID` =12;