Very Simple. Is "we" 2 people? 3? 4?
TAXI -- Up to 4, taxis are a flat fee from Airport to Hotel in Central Athens -- 35€. This covers luggage, tolls etc. You can tip 1€ or so on top of that, but if driver asks more, just say no. At midnight, fare goes up... is around 55€. Time -- about 45 minutes outside of rush hour... about 1 hour in rush hours.
Because you don't specify which hotel, only "near acropolis," cannot give full advice for getting you direct to door by public transportation (specific is always best), but here are the 2 methods. And here is the Metro Map (click to enlarge) http://www.ametro.gr/files/images/AttikoMetro_Athens_Map_eng_LG.jpg
X95 Bus -- This goes 24/7 every 20 mins or so from right in front of Airport Building (there is just One building). During daytime, you buy ticket at a kiosk/counter by the door. At night, in the bus. Fare: €5; there's a Senior discount of I think 20%. Your luggage goes inside the bus, in a central "pen." You must "validate" (punch) your ticket in a pole-mounted box inside bus. From airport to termination point in Syntagma Square, no one can get ON bus, and only 2 hotel stops where anyone gets off ... so this bus is pretty much pickpocket-free. Takes same amt of time as taxi. When u reach Syntagma, it's end of line, so you don't have to rush getting off, and you disembark right onto sidewalk by the TOP of the square. This is my preference, because I'm usually exhausted from allnight flight, and can droop & drowse en route. My hotel is also near Acropolis, about a 10-15-minute walk, but it's "downhill" along Amalias Avenue, so I don't mind it, pulling my roll-along bag.
METRO -- From front of airport, follow crowd across street, up escalator to Metro Blue Line platform. Buy ticket at window (€8 for 1 person, 14 for 2, 20 for 3, half-price for seniors). Metro starts there, about every 30 mins, takes 45 minutes to Syntagma. Empty at beginning, is very crowded by time it reaches Omonia/Syntagma... and doors are open only briefly so you must be ready to get off promptly. ALSO NOTE -- This Metro, and the Green Line (to the seaport) are the ones targeted by really skilled pickpockets ... mainly because they're filled with US tourists, many of whom never take public transit at home and are gazing around, not alert. Do NOT carry money, credit cards, passports in pockets! Use moneybelt or (for women) your zipped daybag, crosswise, hand on zipper. Do NOT let your husband disobey this (most victims are men, who say "i'd know if anyone touched MY pocket!" and afterwards can only say "oops").
TO HOTEL -- If your hotel is on SOUTH Side of Acropolis, you could get off the Blue Line at Syntagma and follow the crowd to the RED LINE platform (see metro map), and take it ONE stop, to ACROPOLIS station.
GETTTING OUT of METRO STATION(s) -- At Syntagma there are escalators to the outside "plaza level", then a ramp where you can roll your bag up to sidewalk level. At Acropolis, there's an escalator up to ticket-window level, but you may have to "bump" your bag up steps to street level, i can't remember.
YOUR HOTEL: -- here's an Athens Map to locate your hotel (click &it gets huge; all street names in our alphabet): http://www.orangesmile.com/destinations/img/athens-map-big.jpg