Generally, bounce rate means someone landed on your site and left, without visiting any other pages. To improve bounce rate you have to figure out why people are leaving. FIrst scenario: Someone landed on your site and did not find what they wanted. Second scenario: Someone got to your site, got their answer and left. In the first case, you are not answering their query, which means your page is not relevant to their search. In analytics you can look at your top Content and see which pages are the most visited. I would start here in order to identify which pages have the highest bounce rate. Make sure those pages give users what they are looking for. Not sure what industry you're in but I don't think 45% is necessarily bad, and bounce rates vary depending if it's a legal site, ecommerce, etc.
In the second scenario, if people find what they want and leave, then identify the action you want them to take. Sometimes, the only goal is for someone to call you and if you have good call-to-actions then maybe this is what's happening. If you are not converting then you have to dig deeper and identify what's going on. (Not certain, but I think you can use Funnels in Analytics to identify how users interact when on your site.) Make sure there are other elements on the page for users to contact you, visit your Facebook page, sign up for your newsletter, etc. Also look at your top keywords and make sure they are on target (relevant) for your pages.
This is assuming your site has good design, structure, etc.