There is nothing wrong with changing the “official” job title on your resume. You're simply translating past experience into the same language as a hiring company. This is what optimizing your resume keywords is all about.
Three examples of when to change your title:
1. You’re applying for a position as a “Content Writer” but your previous job title was “Content Creator.” The hiring manager will likely search “Content Writer” in hopes of finding someone with direct experience. It’s the same job, so change “Creator” to “Writer” on your resume to increase your searchability.
2. The job title buzzword fad (ninjas, gurus, rock stars et al) is thankfully dying out but what if you still have “Customer Service Wizard” on your resume from a previous job? Unless a job description asks for actual “sorcery” skills, change the experience on your resume to something that reflects the new job for which you’re applying.
3. You worked for six years as the Web Developer at a small firm that didn’t differentiate experience levels. In other contexts, you would be a “Senior Web Developer,” so make that change on your resume as you pursue other senior-level positions.
Important note: This is about re-contextualizing your work experience rather than improving it. Don't give yourself a promotion that didn’t exist.