I like my computer keyboard but the letters have nearly worn off

A late answer having run into the same problem. I have a new keyboard ready to use but this one still functions well, apart from the worn out lettering. I can wring a little more life out of this one with a hack.

• By swapping the key tops around.

Replacing the worst keys A, S, N, T with function key tops.

A ~ F4 (the 4 is like an A)
S ~ F7 (the Seven initial)
N ~ F9 (the Nine initial)
T ~ F2 (the Two initial)

There is no confusion with the function keys because they run consecutively and I did not use any adjacent ones.

I carefully prised off the key tops with a screwdriver and pressed them back on after correctly aligning. Gently, because the small plastic clips/hooks are not vey strong.

Edit: after some usage I revised the scheme so that all the replacements resemble the shape of the letter, and this was easier to make the connection.

A ~ F4
S ~ F5
T ~ F7
N ~ F11

You may use a correction pen which usually lasts for a long time.

I've used this on my keyboard and it really worked.

I use self-made stickers, which can be used for at least 3 months each time.

So this is a USB device. Right?

For every USB device you can find out the USB manufacturer and probably model. Here is how it could be done in Windows. In Linux this can be done using lsusb command.

Having manufacturer and model you can search e.g. on amazon or any other such service for the same keyboard/set. Probably you can find used ones or even broken ones to get spare parts (keys) from them.

By accident I discovered the search term "keyboard stickers"

I found a selection on Amazon that look like the ones on my keyboard. They're not expensive so I've ordered some.

The reviews say they are durable so here's hoping!

Update: They arrived from France and are good quality. The only disappointment is that a sticker for the left-hand Shift key wasn't included.

Update 2: It's now 5 months later and they are still in perfect condition.

My Hack was inspired by Weather Vane.

Replace the letters on the keycaps of the keyboard you have come to love.

White Sugru™ mouldable glue would be wear resistant and highly visible against the dark plastic background on your keyboard for the most-used e_t_a_o_i_n_s_ keys, if not all.

• You would etch the shape of the letter into the keycap with an engraving tool.

• Push the white Sugru into the hollow channel and let it cure.
  Use a little more than enough to fill the gap.

• After it has cured a while (according to the instructions), remove the excess so that the Sugru is flush with the keycap.
  It will continue to cure becoming more resilient with your tapping.
  It won't rub off as would anything applied to the surface. It becomes part of the key cap.

If you don't feel confident wielding an engraving tool freehand, visit an engraver where trophies and name plates are personalized with an engraving machine. The size and style of the letters is adjustable. It is very precise and consistent.

It probably won't be very expensive.

Good luck.

Frame challenge answer:

Instead of replacing the print, learn to type without looking at the keyboard keys. There are lots of (free) tools available and with a bit of practice you should soon be able to make good progress.