how do you pay a ticket 6 yrs old to renew license CA?

You'll need to get any fines paid off and clear any failure to appear. That will take a visit to the court where your citation was issued.

Get there early, stand in line, explain this to the clerk and ask to have your case put on calendar in front of the judge so you can get it cleared up. Once any fines and failures to appear are cleared, the DMV should be able to reissue your license.

As counsel above indicates, you must start at the clerks office. You may or may not be allowed to pay it off without a hearing, but the late penalties may be exhorbitant. Once this is done the clerk will provide documentation to bring to the Department of Motor Vehicles to lift any suspension which may have been entered. These are two separate agencies and they must both be satisfied as to their requirements. Putting these things off only hurts you.
Good luck

The attorney does not practice law in California but provides this answer as a guideline.

If you have never contested the ticket and do not wish to contest the ticket, you can clear the matter by posting the bail and collection or failure to appear fee with the clerk of the court. The clerk can look up the case and give you an amount. If you wish to contest the matter, you or an attorney can appear, plead not guilty and have the case set for trial. After the appearance, you can generally pay a small fee to the clerk to show that the failure to appear has been cleared. With the failure to appear cleared, you can go to the DMV and get your license. DMV may require a $55.00 re-issue fee, if your license was suspended for failure to appear or failure to pay. In such an old case, there is a reasonable chance of being found not guilty at trial either because the officer doesn't show up or because he shows up and doesn't remember any of the details. If you previously plead guilty and failed to pay, the fine will have to be paid before your license is cleared.