1994 Honda Accord slipperage in 4th gear and reverse

Over the past 9 months my automatic transmission will occasionally not engage in to 4th gear for several days and then return to its normal operation, the same for reverse. The trans oil is still the manufacture original product, it is light brown in color now but it does not smell burnt. As I would like to change the trans oil and its filter myself however I have been advised that the transmission must be separated and pulled down to local the filter at the end of the transmission body. And, that this is NOT a job for a non experience person. So, do you recommend that I have the trans-oil and filter changed by a pro? Can I do this myself? OR, run the car until the transmission goes for it is too late.