Lord Hanuman with Aṇimā and Garima Siddhi

In the Ramayana Hanuman changes shape several times. For example, while he searches for the kidnapped Sita in Ravana's palaces on Lanka, he contracts himself to the size of a cat, so that he will not be detected by the enemy. Later on, he takes on the size of a mountain, blazing with radiance, to show his true power to Sita.

Also he enlarges & immediately afterwards contracts his body to out-wit Sirsa, the she-demon, who blocked his path while crossing the sea to reach Lanka. Again, he turns his body microscopically small to enter Lanka before killing Lankini, the she-demon guarding the gates of Lanka.

He achieved this shape-shifting by the powers of two siddhis; Anima and Garima bestowed upon him in his childhood by Sun-God, Surya.

Lord Hanuman with Anima and Garima Siddhi

• Aṇimā: reducing one's body even to the size of an atom
• Garima: becoming infinitely heavy

The following are the eight siddhis (asta-siddhis), 

• Anima 
• Laghima 
• Mahima 
• Garima 
• Prapti 
• Prakamya 
• Vashitva 
• Isitva 

These are basically to control to five elements, “paanch mahabhoot” (prithvi, jal, agni, vayu, akaash).

Footprints of Lord Hanuman : 

In Srilanka, a stream that runs from the hill, catered to the needs of Sita devi during her stay at Ashok Vatika. She is said to have bathed in this stream. Now there is a temple(Sita Amman temple/Sita Eliya) of Lord Rama, Sita devi , Laxmana and Hanuman by the side of this stream.

It is interesting to note that foot prints akin to Lord Hanuman's are found by this river and some are of small size and some are of large size, which tells us of the immense powers of Lord Hanuman transforming himself into any size.

Jai Sri Ram