I Need Advice on Key Word Density Reduction

Some years ago, when Google did not have new keywords rule; my website was ranking very well (on the first page) for several key words (k.w) but since they've changed to the new seo rules about keyword density, my website dropped to 2nd page or 3rd page; I got advice from some seo people that I should reduce my existing keywords density so I've been doing the keyword reduction on my Magento site but I'm not sure if I do it correctly.

For example, I reduce keywords in the product's heading (in General/CMS):

Daydream Island Twisted Bandeau Plus Size Swimwear | One Piece underwire | Swimwear Online (original heading/name)
The URL key for that product: daydream-island-twisted-bandeau-plus-size-swimwear-one-piece-underwire-swimwear-online

Now if I reduce the k.w as below:
Daydream Island One Piece Plus Size Swimwear Underwire

Should I change the URL key as below as well?
daydream-island-one-piece-plus-size-swimwear-underwire

Because if I only change the Name but keep the URL key as its original, the URL key is still long with many k.w?

Please advise if I should or should not change the URL key as above?

I don't know if the changes (reduce kw) would affect the indexing. After every time I reduced kw of the products pages (changed products' names; title tags; meta descriptions); I always generated the sitemap.xml (in the CMS as well as in Google webmasters tool Crawl>Sitemaps). Should I fetch the website to GG sometime too?

I look forward to your reply and thank you very much!

P.S: I got advice from someone as below

<<<Please do not change any URLs. Just edit the heading, title tag and meta description to make them natural.

URL key - Do not change

- Product Heading/Name: DayDream Island Twisted Bandeau

-Title Tag (in Meta Information)

Day Dream Island Twisted Bandeau Plus Size Swimwear Underwire

- Meta Description (in Meta Information)

You can create this with the combination of product description and keywords>>>

Are the above advice good? For the Tittle tag, should I put the product name "Day Dream Island Twisted Bandeau" as a part of the title tag (in Meta Information/CMS)?

keyword density is best option to promote your website in google search engine. you should keep 2% keyword density in your website for better promotion.

There is really no such thing as “ideal keyword density.” On different occasions, webmasters have contacted me and asked what I felt the ideal keyword density is for their particular site or webpage. This question can only be answered on a site by site basis, however more times than not, keywords usually only have to be used a few times per page. When I optimize a website, I usually place the page’s focus keyword in the title tag once, in the page content 3-5 times (depending on the subject), and 1 time in the meta description. If you have good, solid content this is usually enough. Matt Cutts, the head of Google’s WebSpam Team, has said that good content will trump SEO every time, so the smart thing to do would be to focus on your copy and on creating good content instead of keyword density percentages.