The very definition of a revocable trust means that you are able to make changes to it in a few different ways. You can, for example, prepare and sign a trust amendment that is valid under your applicable state law. 
This makes an amendment or an update to the existing trust so if further substantial changes are needed you might wish to revoke the original trust agreement and create a new trust. The second option available to you is to sign a complete trust restatement valid under your state law.
Your third option is the most expensive, time-consuming, and radical. This involves revoking the original trust agreement and any amendments, then transferring the assets that were stored in the revoked trust back into your own name. You could then create a brand new revocable living trust if you wanted. This third option might only be required if you are making significant changes to the initial trust agreement.
In most cases, restatements or amendments are appropriate if you just wish to add or change beneficiaries, if you divorce or if you marry or have a child. Make sure that you have a relationship with a trusted estate planning lawyer to protect your best interests.