And this pre-supposes that you edit files and will dive into what SRT files are.
SRT files for example are widely documented such as https://www.google.com/search?as_q=srt+editor so there should be no questions about sub title editing.
Now you can alter the times as you wish, re-create the DVD and you're done.
I've got DVD video disc where I feel subtitles are displayed little too late. Is it possible to finetune appearance of subtitles to little earlier?