I travel from/through MAD often. There is a free bus on the lower level of T4 but it is slow and the frequencies are not constant. You can take the metro to T1T2T3 but there is a 15-minute walk to T1 from the metro drop-off. So I would recommend, depending on timing, see if the bus will work, if not the only option so you don't miss your flight is to take a taxi from T4 to T1....it should be on the meter but I'm not certain... this would by far be the best option and should be less than 8 minutes terminal to terminal and you can be dropped off in front of the EasyJet check-in. Good luck.