There are 16 possible results in 4 tosses of the coin:
HHHH, HHHT, HHTH, HHTT
HTHH, HTHT, HTTH, HTTT
THHH, THHT, THTH, THTT
TTHH, TTHT, TTTH, TTTT
From this we can see that one head or fewer occurs in just 5 cases: HTTT, THTT, TTHT, TTTH, TTTT. That means that in the remaining 11 cases heads occurs more than once, giving us the probability of 11/16=0.6875.