check via your Android's google playstore if Mobileuncle is available for your device.

install it and before running it download and unpack either the TWRP or CWM zip file for your device

rename the enclosed RECOVERY.IMAGE file as recovery.img and put it at the root of your internal storage (if rooted phone) or the root of your removeable storage

now run mobileuncles and click on update recovery

it will find your recovery.img and you then choose it.

I recommend TWRP

a short youtube movie shows it in action

this does not need any flashtool......so is very handy for Linux users