Get a manual for you car and read it carefully.
I suppose the valves could be adjusted without the wrenches but it would be very difficult. No oil change is required to adjust the valves, btw. The wrenches are angled to get around everything in the way.
If your valve is turning, stick a large screwdriver next the the valve collar to hold the valve in place while adjusting. A helper is real handy to measure the valves while you are adjusting the nuts. Also it's better to make the valves too loose than too tight.
Look up additional posts on this site (search valve adjust). They will list some shortcuts to make the job easier.
Good luck.

__________________
Rev. Dr. G. Church of the SubGenius
It doesn't take a genius