Leverage in MetaTrader terminals cannot be changed manually. It is set by default for all instruments according to the Instrument Specifications, but it may adjust automatically under certain conditions:
Weekend leverage reduction: Every Friday from 20:00 to 21:00 GMT, leverage is reduced by one or more levels for all existing and newly opened positions. For example, for FX Majors, it may be reduced from 1:1000 to 1:500, and for Energy CFDs from 1:200 to 1:100 (excluding Stock CFDs). It is important to note that the Stop Out level is also lowered during this period from 50% to 0% as an additional measure to protect your positions from sharp price movements.
Total position volume thresholds: Leverage changes automatically upon reaching a specific total volume of open positions for a particular instrument (see more details in this article). Volume and leverage are calculated individually for each instrument, not for the entire asset class.
Account manager request: Leverage can be adjusted upon personal request to your account manager (for example, to enable publishing your own trading signals).
These factors should be taken into account when planning your total position size and when keeping positions open over the weekend.
You can find more detailed information about leverage via this link.