I have a 7 speed freehub and would like to upgrade to 9 speed. My frame has 135mm spacing. I dont think the freehub is Shimano because a 10mm allen wrench does not fit. I have a Sram 7 speed cassette currently. Will a Shimano 9 speed freehub fit? Will any modifications need to be done to the wheel?
If the freehub is not by Shimano then the freehub body cannot be exchanged with a Shimano one (well, most probably). Does the hub have any manufacturer markings on it?
Other options: replace wheel with new hub (only if rim is still very good -> they are consumables, after all) or get a new rear wheel.
What brand is the hub? If it's shimano, the freehub should be shimano. Have you tried putting a 10mm allen in after removing the axle? You say it doesn't fit but also say you don't have the right allen wrenches. If it is another brand hub, you should be able to research from there how to swap the freehub.