There are different ways to change your visa from temporary visitor to any other visa in Japan. However, the most proper way is applying for Certificate of Eligibility first, before the visa.
This goes for any type of visa you want to change. For example, you are a foreign resident in Japan under working visa and you have a fiancé with temporary visitor visa and want to be with him/her in Japan. However, there is no fiancé visa in Japan. There is dependent visa for spouse or children. You have two (2) options on how to get him from abroad and have him stay with you in Japan.
First option is you can invite him/her as temporary visitor visa and you can get married here in Japan. After getting married, you can apply for change visa from temporary visitor to dependent visa.
Second option, you marry him/her here in Japan or abroad, he then goes back to his/her home country. Then you apply for his Certificate of Eligibility. Once received, you send it to your fiancé abroad so that he can apply his visa with Certificate of Eligibility.
Another thing you should know about changing visa, especially working visa, one must not work or engage in activities outside their current visa.
If you are trying to apply a different job, then you must apply for change visa first before getting involved with that job. For example your current visa is designated activities and your current job is housekeeping, but you want to resign and look for a different job. It is not against the law to apply for a different job while under a certain visa. However, if you are simply seeking for a new employer, but same job, then you don’t have to change your visa. If you have found another job and your new employer is willing to sponsor your new visa, then you must go ahead and apply. Once you receive your new visa, you can no longer engage in activities of your previous visa. You can now only participate in activities permitted in your new visa.