The answer depends. It depends on your budget, your expertise, how much time you are willing to spend, your goals, the mission of your company and a lot more. Generally, a good audit will help you understand your goals and help you get started in the right direction. If the audit makes sense and you are willing to trade money for time, hiring a specialist is a good option. Allocate $3000/month for a 6 to 8 month campaign. If you have a limited budget, then just hire someone to do a thorough audit of your website. Budget $1500 for an extensive indepth audit. If the audit is done correctly there should be actionable steps you can work on to boost your SEO rankings. Follow the instructions in the audit. Expect 3 months to see results.