easyp on "function override"

I'd like to override a function in woocommerce, specifically -
woocommerce/includes/wc-cart-functions.php (the wc_cart_totals_order_total_html function).

I could edit the function directly (it outputs html that needs to be changed), but I'd prefer not to as I'll lose changes on updates.

I'm sure it's a common thing, I'm just not quite sure how to go about doing that. If I copy the function to functions.php in my theme, I get an error about re-declaring the function.

thanks.