Removing windows 10 from dual boot and hard disk space management

I have a dual boot machine with win10 and ubuntu mate 16.04.02. Now I want remove win10 which occupied nearly 100GB Hd space. UbuntuM has 50 GB including 4 GB swap. Please tell me the procedure how can I remove win10 with out harming UM. What will be better if I merge the free 100gb with ubuntu partition or keep it as a separate partition. Please suggest. Thanks

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