Which Marlin firmware version do I have on my RepRap printer?

I have a RepRap Prusa i3 that I built from a kit, so I never had to do any firmware related stuff.

I'm sure the Marlin firmware that's in my printer is not current, and I want too check if it makes sense to update it.
But before that, is there a way to check which version is installed on my machine, and what's out there now?

I was thinking that when I first connect to my printer with Repeiter, the firmware spits out what version I am using. However I am using Repeiter FW, not Marlin, which I though also had more than just 1 flavor.

If that doesn't work for you, contact the vendor.

Send M115 to the printer and it should report the current version.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

Thanks @dkarma.

Sending M115 returns the following information:
FIRMWARE_NAME:Marlin V1; Sprinter/grbl mashup for gen6 FIRMWARE_URL:[www.mendel-parts.com] PROTOCOL_VERSION:1.0 MACHINE_TYPE:MakerFarm EXTRUDER_COUNT:1

I'm trying to understand what's the up-to-date version of Marlin now. The page at http://reprap.org/wiki/Marlin says the current version is v1.0.0, which links to a Tagged version on GitHub: https://github.com/ErikZalm/Marlin/tags - this was created a year and a half ago.
Is this the recommended version of Marlin?

Thanks.

This link will take you to the current main branch of Marlin: [github.com].

If you look to the top left of the page, immediately below the number of commits there is a green button. To the right of that is a combo box which will allow you to select either the development branch, stable branch of main branch ("development," "stable" or "Marlin_V1" respectively). Use the main branch. Updates are reasonably frequent.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

Thanks for the info. The link to https://github.com/ErikZalm/Marlin states that Marlin has moved to https://github.com/MarlinFirmware/Marlin.
In the new location the branch dropdown only contains 'Development' and 'master'. Which is the recommended branch to download?

Also, is there an official version number (e.g. 1.0.13b) that increases as new releases are cut (e.g. from the dev to the master branch)?

Thanks.

If looking at the marlin program itself, where does it say the version?