I always wear 8W in open-toe shoes, and 8 1/2M in other shoes (6 in men's, which is a woman's 8). Almost all the comments on Clark's shoes say they are true to size. I ordered 8W and they are WAY TOO BIG, a whole size too long, and the top velcro adjustment above the arch is way too loose and cannot be adjusted tighter so the shoe slides off when I tried to walk with them. I have a normal arch, they have the velcro sewed on for VERY HIGH arches. I also ordered 2 other Clarks' leather open-toe shoe's from Amazon, same size 8W. The Clarks Women's Lexi Bark Slide Sandal is too large also, too long and too wide, unable to adjust tighter. I will return them. The Clarks Women's Truffle Sandal fit ok in the length (about 1/2 size too long), I was able to adjust the velcro as tight as it can go and they seem to be ok to walk, they stayed on. I decided to try to exchange them for a smaller size if they have my size, because when the leather stretches they will definitely be too large.
I'm not sure what size to replace the Clarks Lena Enjoy with, so I called ShoeMall for their suggestion. They 'suggested' to replace with size  7 1/2 M. I will try that size and will let you know how they fit. I hope they do because I really don't want to have to return another pair that doesn't fit at my cost.