I'm trying to model the letters K and S from a picture that my friend sent me (below), and I modeled the letters but I'm having trouble figuring out how to smooth the edges so it's not so rough and bumpy! I also want to make the letters feel more bubbly. Thanks!
For this type of illustration work you may want to consider using bezier curve objects instead, they allow fine grained control over the curvature of your objects. And you wont have to worry about triangulation or tessellation of the top and bottom faces.
They allow easier control of curvature and guarantee smoothness, and also allow easy non destructive beveling too.
Perhaps even draw them in a dedicated illustration program like Inkscape and import them as SVG into Blender
Be mindful about very tight or sharp corners inside the the meeting point of the K arms they may cause trouble with beveling
Also have in mind that they have downsides and will be more limited in other aspects if you later want to do more processing. They wont work well with subdivision surface, they have more limited texturing and material capabilities. Some of these limitations can be lessened by duplicating the objects and converting the copy to a mesh later.
Try the Subdivision surface object modifier. Go to the Properties panel > Object Modifiers tab and choose the Subdivision surface modifier from the drop down menu. Use the View: value to control the 3D Viewport subdivisions and the Render: value to control the rendered subdivisions. It should look something like the following.
This will definitely soften some angles, but it will also likely negatively affect the shape. To retain some of the shape, you will want to add Loop Cuts with Ctrl + R. Loop cuts will appear as pink loops and you can move your cursor around your model to have Blender suggest different directions for them. You can LMB to confirm. Once confirmed, you can drag them around to weight the angles of your mesh that you want to keep. There is a video further explaining them here.