when doing seo on an existing old site can i change the old permalink structure to a new form or is this bad?

[EH3fG3FtG0]

Hi I have just basic seo knowledge, and are wanting to know the following:

My client has a site that is over 10 years old, they pay a current seo company to do backlinking and article submission, but no onsite seo optimization, except for existing permalink structure. The current structure is this hxxp: //sitename.com/year/month/page-title-basic-keword-optimised/ . (Day and name)

They have a product in the manufacturing industry that although the product gets improved never gets old and they don't like the dated look of showing year and month.

If I change the permalink structure to just Post name or category-name/Post name what implications would this do to their existing rankings? And if I apply good 301 redirecting of old posts to the new location, will this work at keeping their existing rankings?

Thanks heaps guys I don't want to screw their site and need your words of wisdom.

[R4g3]

As long as you redirect everything and the backlinks are not pointing at 404's and update the sitemap + fetch/index in webmaster tools it should be fine.