Most likely you can do it in parallel with your current job, but you'll have to reprioritize your daily routines. For instance, I had to give up on a big part of going out for 3 months to find time for interview preparations.
Quitting your job to speed up the process is also an option, but keep in mind that:
- Some areas, like responses from recruiters, interview feedback, visas, etc do not depend on you. Those are impossible to speed up.
- We tend to underestimate the time needed for a job search. If you think that you can make it in 4 months, make sure you'll be comfortable staying without the paycheck for 8 months.