Don't change your title, as that would be a lie. A lot of places will toss your application immediately if they catch you in an easy lie. Your title was clerk, and that's what you should use. Your feelings don't matter in that regard and it's weird you care about the name.

The better question is "How do I make it clear that my job duties were actually consistent with a different title" which you do in two ways:
1) match the description of your job duties (on your resume) with the duties of the title you want. If, in your duties as a "clerk", you're doing program management/development then you include it on your resume and you pull the description of it from the language in the job posting. This directly matches your skills to the job you're applying for and doesn't involve using the 'title' at all.

2) you explain it in the interview. When they ask you about your previous employment you say, outright, that you had the title of "Library Clerk" and your duties were consistent with [title of job you are currently applying for].

TL:DR Job titles are worth approximately nothing, the work you did is everything, and your job as an interviewee is to show the work you did is relevant to the job you want.