Download falls in Class 9, software & electronics, and depending on what exactly you sell it can also fall in Class 42 or Class 41 or Class 35. Everything below is read from the USPTO's own list of accepted descriptions, not from an opinion about where it belongs.
Searching the USPTO Trademark ID Manual for download returns 400 accepted descriptions, and most of them sit in Class 9. The manual is the list of identifications the office has already approved, so wording taken from it is pre-approved and settles the class at the same time.
The class follows from the identification you write, so "what class am I in" is really "what exactly do you sell". How the class system works covers the rest.
Software, apps, downloadable content, computers, or electronic devices.
272 accepted descriptions in the manual mention download. For example:
Software as a service (SaaS), app development, IT, design, or science and engineering services.
59 accepted descriptions in the manual mention download. For example:
You teach, train, publish, coach, or provide entertainment, events, or media content.
54 accepted descriptions in the manual mention download. For example:
You run a store, sell advertising or marketing, or provide business and office services.
9 accepted descriptions in the manual mention download. For example:
Download appears in 4 classes because what you make, what it is made of and the service of selling it are separate classes. Pick the descriptions above that match what you actually do.
Making download is Class 9; a shop or online store that sells it is retail store services (Class 35), and a business that does both files in both.
Software and electronics. Downloadable software is here, but software as a service is Class 42, and many software businesses need both. The split reaches as far as straps: watch straps are Class 14, smartwatch straps are here.
The class decides what a registration covers; it does not decide whether the name is available. Relatedness is judged on the identifications, so a conflict can sit in a class you never looked at: the same name in a different industry.
Check whether your name is clear for download Searches the live USPTO register, including sound-alike and meaning-alike names. First search $2, then $5.Download sits in Class 9, software & electronics. That is where the USPTO's own ID Manual puts it: 272 accepted descriptions mentioning download fall in Class 9. Depending on exactly what you sell it can also fall in Class 42 or Class 41 or Class 35.
You file in every class you actually use the mark in, and the USPTO charges its fee per class. Selling a product and also running an online store for it is two classes, not one. Filing in classes you do not use is worse than filing in too few: an application has to be supported by real use or a genuine intent to use.
No. The class decides what a registration covers. Availability turns on whether someone already holds a similar mark for related goods, and relatedness is judged on what the identifications say rather than on the class number, so marks in different classes can still conflict.
Not what you sell? Search the class finder for your own wording, or browse all 45 classes.