I want to read tenfold faster than now = I want to read ten times faster than now
Can I use the word 'tenfold' in this way?
I suppose you can, but if you check tenfold examples you will see most examples involve increase/decrease or rise/fall (change words rather than static state ones).
For your example, I would stay with "ten times" Using tenfold this might be better:
I want to realize a tenfold increase in my reading speed.