Coolant problem

Hello guys lately i found that sometimes when i check the radiator is empry or with very little coolant and all the collant stays at the overflow tank .. other times is full without touching it or filling it.  No overheating problems at all and engine working perfectly .. i have changed the radiator cap .. I found that the freezer plug is leaking a little bit. Could this be the problem that i don have much coolant in the radiator and all of it goes to the overflow tank ?
M13A engine manual 2002

Any leak in the cooling system can prevent the vacuum necessary to pull the coolant back from the expansion reservoir, so yes, the freeze plug could be the cause.

Do you know what i have to do and how can i change this freeze plug ?

They are commonly called "core plugs" so your first job is to find one or a set for your engine.
To change them first drain the coolant. Then  remove the old core plug, a screw driver punched through it can be used as leverage to pull it out. Clean the alloy hole with Emery paper. Smear sealant (blue hylomar or similar) lightly around the new core plug and use a socket just smaller than the core plug to lightly drive it home. Don't push it so far that it falls inside the water jacket, just enough to seal.
The garage "cheat" is to just drive the new core plug home without removing the old, but the old plug just ends up inside the water jacket, not something I would do.
Now the big problem with all of this is just how much access you have to achieve the above. Usually the core plug is not accessible and requires the engine out, or if you are lucky, a few other items need removing to allow access. I can't tell from the photo how lucky or unlucky you are!
The boge is to cover the leaking plug with liquid metal expoy resin. It will work for some time, but is no substitute for a proper fix.

Fordem is correct, this slight leak could cause issues. The Jimny cooling system is, as I like to say, a spit and suck system. As the water expands it is pushed "spit" into the bottle. As it cools it is sucked back. Any leaks will reduce the ability to suck it back, hence it slowly empties the radiator as it spits the coolant into the expansion tank.

So if i seal the round of the core plug with liquid exposy resin that will fix my problem for some time you say ?

Based on personal experience, it's unlikely to be a "long term" repair - it depends on how frequently the vehicle is used, you'll get a few "heat cycles" out of it - the expansion & contraction will loosen the epoxy.