if you have access to the database you can go in there and create a new for yourself, if not then the developer of your site will have to do it for you.
in the database find the wp_users table, find your entry and click edit. scroll down until you find the password box (don't worry about it looking like gibberish, it's encrypted), delete what's in there, add your new one and then in the dropdown menu next to the password text box select MD5 as your encryption, click save and then you're done.
go back to your wordpress site, refresh the browser, try logging in with the new password and you should be fine. remember to write the new one down! :D