need to change 1990 timing belt. 160,000miles. do i have to loosen or remove oil pan or anything that reqires professional only?

I don't believe you'll need to loosen the oil pan. However, this vehicle has a timing chain, not a timing belt. You'll want to get a Haynes manual or else pay a professional to do it, around here it would be in the $350 range for the whole job.

I did this on my 88. Replaced the chain, tensioner, crank and cam sensors (crank sensors are known to go bad on these engines) and of course the timing chain and sprokets. Oil pump while I was there, all new gaskets including intake, valve cover and oil pan gaskets. The front three oil pan bolts, harmonic balancer (36mm bolt) and timing cover need to come off to do this job. Not too bad if you're mechanically inclined. Haynes manual would be helpful