1995 Honda Civic Stuck gear

Back again this car is driving me nuts :D. Ok basically my car is not upshifting. I let it warm up, usually happens when im at a stop and have to go. My car seems to get stuck in 1st gear. As far as I know the transmission oil filter has never been changed so it may be clogged making the criculation poor. Im gonna change that first. Engine light is not on. Do you guys have any more alternatives, computer, torque converter. Whatever you can come up with that's solid please let me know. Thanks so much for taking the time to read this question, take care.