I read somewher that you should prune it in early spring, and in another place I read it can be pruned any time. You can prune up to 1/3 of it. It can be fertilized once a year in spring.
If this is Euonymus alatus 'Compactus' or any form of E. alatus the branching habit does not allow much heading back without an ugly effect being produced. Vigorous specimens planted where there is not enough room can be cut to the ground at the end of winter periodically to renovate. Do not do this every year, only when the plant is again "too big." Fertilize if a soil test indicates a deficiency. Fall is the best time to fertilize hardy plants such as this.