City and mountain bike tyres go on and off by hand as easy as Tupperware tops. Narrower road or touring tyres don't. Sure, with decent tyre levers, a bit of thumb strain and a dusting of talc, anything's do-able. But easy? Not always. If you're having trouble, try a Speedlever (now available again in the UK).
Instead of two or three levers, you just use one. It hooks under the tyre bead (removal) or over the rim (refitting), and the lever telescopes down to clip over the axle. By rotating the extended lever around the axle - like the second hand of a clock, but usually faster - you force the tyre off or onto the rim. It takes a bit of effort to get it going to remove a tight-fitting road tyre, but refitting works like a charm.
You just need to be careful not to catch the inner-tube and drag it round inside the tyre, forcing the valve over. (This only happened to me once.) It worked fine on a 23mm tyre and fatter ones were trivially easy. I couldn't get it to fit a 25mm Schwalbe Marathon Plus at all, but to be fair that usually takes two Pedro's Milk Levers, two toe-straps, and plenty of cursing. The Speed Lever is made of tough polycarbonate and has a lifetime warranty.