Bicycle Mechanics - Saddle changing question

I'm considering switching out the saddles between the bikes I ride on the one I ride the most since that saddle is really uncomfortable and hurts. I've never done it before, but I'm pretty sure I can do it myself as opposed to paying my lbs $30. I attached pictures of them and was wondering if it was possible to switch the two or at the very least add the more comfortable seat to my bike? If not, could someone recommend me one that would work or a gel seat?

Thanks!

Alright thanks!

Okay I tried it, but ran into a problem. The black seat has rails, but they are much bigger than the one the brown seat uses so they won't clamp on when I tighten the bolt.



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The second set of pics would have been more helpful to begin with. The two saddles are NOT compatible with each other. One has flat rails (right thumbnail) and the other has standard round rails (left). Most saddles these days use the style on the left. You have a different clamp and saddle on the right. Your seat posts are also different. The one on the right uses a collared clamp to secure saddle to seat post. The one on the left uses a single bolt integrated clamp.

There is the possibility that you can measure the seat post diameter of both bikes and if they are the same, then you can swap the whole seat AND seatpost. Otherwise, you'll need to get a new saddle clamp for round rails and check the top diameter of the clamp so it conforms to your bare seatpost.

pentahedron: If as suggested above you try to swap seat posts be aware that they come in 0.2mm increments (about 0.008") so you will need to measure precisely. Many posts are marked with the diameter below the min. insertion line. If the post is too large it will not fit into the seat tube, if too small it will not clamp securely and you could damage the seat tube clamp mechanism if you try to "crank" it tight.

Alright. Well I guess I'll just try getting a new seat. I don't want to mess with the other seat posts from my other bike since it's rusting. Would any modern seat work on my bike like these:

http://www.amazon.com/Zefal-5627-Tru-Gel-Bike-Seat/dp/B0040QCE7M/ref=sr_1_4?ie=UTF8&qid=1317092518&sr=8-4
http://www.amazon.com/Avenir-Mountain-Saddle-Black-Silver/dp/B003RLHGMY/ref=sr_1_6?ie=UTF8&qid=1317092518&sr=8-6

Sorry if it seems like I'm asking a lot of questions, but I want to become more familiar with how a bike is built so I don't have to blow money at a lbs doing low maintenance when I can do it myself.