Look for Teaching English as a Foreign Language (TEFL) or Teaching English to Speakers of Other Languages (TESOL) qualification courses close to where you live. Oversea employers see both qualifications as equivalent to each other, so it does not matter which one you get qualified for. You can also sign up for classes on line.
Complete the courses in as little as a weekend, if you are taking them in person. Online courses take anywhere from six to eight weeks, and you have six months to complete the program.
Look for teaching opportunities on websites such as the Folkuniversitetet, which is one of the main educational institutions in this country. Most courses for adults begin in September, parallel to when the school year begins in Sweden.
Check out The Study Promotion in Sweden. It promotes continuing education for adults and is where you can find openings for English-teaching positions.
Make sure to apply for a work visa before you go, but only after you have secured a teaching job in Sweden.