Why MP3 to M4A, for this MP3 file
iPhones and Apple Music style apps expect M4A, which is AAC in an MP4 audio container.
The M4A sound you will actually get
The MP3 is encoded as AAC and saved as M4A on your device. It is not higher quality than the MP3.
A voice memo that is already M4A does not need this. Keep the MP3 if Windows users also need a copy.
When MP3 to M4A is the right page
MP3 to M4A sits on this site because MP3 and M4A are not interchangeable, even when they look similar in a file list. iPhones and Apple Music style apps expect M4A, which is AAC in an MP4 audio container. Podcast hosts, cars, WhatsApp, and old speakers expect MP3. Apple Music style apps expect M4A. WhatsApp and Windows often want MP3 instead.
The MP3 is encoded as AAC and saved as M4A on your device. It is not higher quality than the MP3.
What you give up by leaving MP3
MP3 is the audio file that plays everywhere. It is lossy. Music is often 192 to 320 kbps. Speech can be lower. Each MP3 save throws away a little more. Turning MP3 into WAV or FLAC does not bring the lost detail back.
Keep WAV or FLAC if you might edit again. Keep the MP3 if it is your only copy.
What you gain, and do not gain, with M4A
The download has to be M4A, because that is the format the next step named. Apple Music style apps expect M4A. WhatsApp and Windows often want MP3 instead. A voice memo can move to MP3 without losing the words.
Convert once, at the end, if you will edit the memo.
A test that matches the real file
Start from the question the other software asked. If it asked for M4A, MP3 to M4A is the matching page. If it asked for something else, switch tools instead of hoping a similar extension will pass. iPhones and Apple Music style apps expect M4A, which is AAC in an MP4 audio container. The MP3 is encoded as AAC and saved as M4A on your device. It is not higher quality than the MP3. The limit is the part people skip, and it is the part that decides whether the download is usable. A voice memo that is already M4A does not need this. Keep the MP3 if Windows users also need a copy. The file stays on your device. The first run downloads a converter, so keep this tab open. A phone runs out of memory on long files. A computer is the safer place for a big clip. Check three things in the download: it opens, the MP3 material you cared about is still there, and the file size or the layout is what the form described. A new extension alone is not those three things. If a portal, a teacher, or a client rejects the file, send them the original MP3 as well when you are allowed to. MP3 to M4A is a convenience copy. It is not a new master. Audio conversions are one-way once the format is lossy. MP3 to M4A can change the container or the codec so a player opens the file. It cannot make a muffled take clearer, and it cannot turn an MP3 into a studio master by calling the result WAV or FLAC. Finish the edit on the best copy you have, then make the share file once.
Here is the decision for MP3 to M4A. You start with MP3 and you stop when a real program accepts M4A. Compatibility is the reason to make an MP3, not an improvement in sound. The MP3 is not higher quality than the M4A, and a new M4A from MP3 is not higher quality either. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
A voice memo that is already M4A does not need this. Keep the MP3 if Windows users also need a copy.
A related step, if you still need one, is M4A to MP3.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.