Four and a half feet at the highest point gives you many options. We build three main types of retaining walls. Timber wall, using 6" x6" treated lumber, Natural stone, be it boulders or quarried rock, and segmental block, which comes in a variety of shapes, sizes and colors.
The most Do It Yourself friendly would probably be the natural stone. There isn't much excavation involved in building rock walls. You pretty much stack them on a decent slope and your done. Don't bother using any type of weed fabric, it's only troublesome and takes away from the look of the wall. Instead, take your time to pick and choose stones that will fit tightly to minimize gapping between stones. When your building the wall, be sure to pack the soils behind the wall, and pack soils into the exposed joints.
Natural stone may be the easiest to install, but treated timbers may be the least expensive, depending on the supply or demand for either in your area. I would not recommend using anything smaller than 6" lumber. Be sure to completely bury the first course. There is really no need for a compacted base with timbers since the weight of the wall has no significance in it's performance. Make sure you stagger your joints as you build up. You can use either lag bolts or spikes. I'll usually predrill with a one inch auger bit about two inches into the wood, then, using a socket and extension, screw a 5" lag bold with a washer into the hole. For the top course i'll use spikes. You''l need to install a series of deadmen in the wall. If your wall is 4.5 feet high, then I would install two rows of deadmen. The first row should be installed in the fifth course, and the second row in the eight(counting the buried course). The buried course will also act as a deadman. I would space them out ten feet apart in each row, making sure that the next course of deadmen fall in between the previous course, that way you'll have a deadman every five feet. Deadman consist of nailing or screwing a 4 foot section of timber onto the last six inches (5.5") of a three foot piece. Don't fasten it right to the end, it will only pull out with time and a little force. Position the T shaped deadman so that the four foot section is on the bottom side of the three foot section. Drive your spike through the top of the three footer into the four footer. eave a spcae in your wall to attach the deadman and your all set. Once you have that first course of deadmen in, backfill them. Make sure you push your wall back about an inch before you backfill, that way, when you backfill further, the force of the soils won't cause your wall to lean outward beyond an acceptable level.
Segmental retaining wall blocks should really only be installed by a professional. If your going to spend the money for the materials, you want the wall to look great. If cost is a factor, choose one of the other options.
I've replaced plenty of cinder block retaining walls. They're not heavy enough to act as a "gravity wall" and there are no graduations or setbacks, to enable them to fight the forces of pressure longterm. If this is a quick fix, do as you wish. But if you intend to stay awhile, i'd advise against light duty lumber or cinder blocks.