If you have had a resume written by a qualified professional recently and just want to update it to include a recent job or accomplishment you can probably do it on your own. If you chose to go this route there are a three guidelines to follow.
Take your time and have a friend or colleague proofread your work and you should be fine. All of these tips have come from errors I have seen numerous times when performing free evaluations for clients.
Check verb tenses. Too often people will update the dates on a previous job, but forget entirely to change the verb tenses in the job details to past tense.
Update your contact info. With the plethora of contact info many of us have such as cell, land lines, emails, and social media accounts sometimes we tend to over share. List a single phone number and a professional sounding email. [Note: If you are still using firstname.lastname@example.org, it may be time to upgrade.]
Rewrite your objective. This is really the key to your update. Your objective needs to be tailored to whatever job you are applying for.