Two methods in their most basic form are:

a) By changing the length (dimension) of the patch.

b) By changing the dielectric constant of the substrate.

if you increase the length then operating frequency shifts towards left and if you decrease the length of the patch then it would shift towards right.

Higher the dimesion of the patch, the greater the frequency will be. So if you will increase the length of patch while keeping width fix, the resonance should move to the lower frequency and vice versa.

Hope this will help you

If the size of the patch antenna ( radiating element)  increases, resonance frequency will be decreases, and if the size of the patch antenna ( radiating element) decreases, the resonance frequency will be increases. Moreover, there are also some other technique to reduce the resonance frequency of the patch antenna, such as DGS, Metamaterial, using slots on radiating element etc. 

Primarily, change of patch dimension (Length) is inversely proportional to the resonance frequency

Apart from this, ABS cover over the patch (It is used generally to protect against weather) creates effect to move frequency towards left (Decrease in resonance frequency).

Other factors already suggested by various people, hence not repeated

If you wished to shift your operating frequency towards the left than increase the length of the patch in TM10 mode and for TM01 mode increase the dimension of the width and in order to shift it towards the right than decrease the dimension accordingly.

It can be done by two methods:

1. Either by changing the dimensions of the patch, or

2. By introducing a frequency tunable active/passive component into the structure, for e.g., RF MEMS, Varactor/PIN diodes and liquid metal (EGaIn) or other fluids.

Thank you for your answers.

How do we implement MEMS structure while simulating antenna in a software?

1. You can increase and decrease the length to move the resonant frequency towards left and right sides, respectively.

2. You can insert slots at edges (increase electrical length and shift resonating bands to left side).

change the dielectric to a low value and it will increase the resonance frequency

Changing the length of the patch will change the position of resonant cz as we know the length depends on lambda and lambda have a direct relation with frequency. Keep the value of dielectric the same cz it is standard. So download the data sheet of material to know what are the thickness of this material that are available in the market and than start your work.

Change the length of the patch 1 mm both sides at one time. you will see your frequency shifting to the right or left.

Besides the length and width of the antenna, hight of the substrate also causes frequency shift.. thicker substrate shift the frequency more towards lower side..

1.by using material having low dielectric constant or

2. by varying the length of antenna

we can change resonant frequency